After feeding inside during its larval stage then pupating, the emerging adult parasite leaves a relatively large round hole in the tiny thrips egg. Make sure to use a pure pyrethrin pesticide, which is considered safe and organic, rather than a pyrethroid pesticide, which includes synthetic chemicals added to increase the effectiveness of the pyrethrin. Relationships of immature and adult thrips with silk-cut, fusarium ear rot and fumonisin B1 contamination of corn in California and Ha-waii. Malchau, W. The preimaginal development of Frankliniella tenuicornis (Uzel, 1895) (Thysanoptera). Certain thrips occur on many different plants but damage only a few of the plant species on which they are found. All contents copyright Susceptible onion growth stages for selective and economic protection from onion thrips infestation. With soil drench or injection, there is a longer time delay between neonicotinoid application and insecticide action. A plant that is badly infected should be removed entirely to prevent thrips from spreading to other plants. Statewide IPM Program, Agriculture and Natural Resources, University of California They graduate to non-feeding prepupae and pupae phases before developing into adults. Integrated Pest Management for Floriculture and Nurseries. Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. ; Greenfield, B.P.J. Background Thrips tabaci Lindeman (Thysanoptera: Thripidae) is the key pest of onions that causes economic yield losses in commercial onion production in Pakistan. (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start': Unfortunately, we cannot provide individual solutions to specific pest problems. Thrips are so prevalent that attempting to control them through the use of chemical pesticides is often counterproductive since it kills a wide variety of helpful insects and may cause local thrip populations to develop chemical resistance. The site is secure. : Influence on Above-Ground Arthropods in the Czech Republic. It is suggested that Bt maize is compatible with the NTAs and provides further evidence of the ecological impact of genetically modified maize. 1 Color does not reliably distinguish among thrips, which can be accurately identified to species only by an expert examination of microscopic characters. Does. Female thrips, which are larger than the males, can reproduce without male fertilization. They are social insects that are usually found in clusters. Thrips, Their Biology, Ecology, and Economic Importance, Global Status of Commercialized Biotech/GM Crops, Thysanoptera Britannica et HibernicaThrips of the British Isles. Adult melon thrips, Thrips palmi Karny. Thrips can survive the winter in the egg stage, which is why removing plant debris is important for thrip control. Maize pests like Ostrinia nubilalis and Diabrotica virgifera virgifera are eradicated using genetically modified maize. The year 2013 was the most numerous of all monitored experimental seasons (. Those based on the application of, The commercialization of genetically modified crops has necessitated an evaluation of the technologys potential environmental impacts, with non-target organisms (beneficial insects, natural pest controllers, rhizobacteria, growth-promoting microbes, and pollinators) among the most likely negative consequences [, Despite the fact that thrips are common in maize fields [, As Thripidae are weak fliers, they spread predominantly through the wind with the host plant seeds (anemochorically). Fewer differences in thrips densities were . What plants are most vulnerable to thrips? Thrips feed and reproduce on the leaves and buds of soybean seedlings. The direct effect on the grain yield was not conrmed. Homes, Gardens, Landscapes, and Turf > Significant differences in maize grain crops were also found between 2013 and 2015, when there was a high abundance of thrips on the plants. Relatively few Cuban laurel thrips can survive the winter outside of the protection provided by the leaves they gall. -. Feature papers are submitted upon individual invitation or recommendation by the scientific editors and must receive Thrips can pucker soybean leaves and silver them when densities are high. Currently, she is a professor of Horticulture, an Education Specialist, and pest specialist. Some organic mulches (e.g., straw) and living mulches (e.g., interplanting the crop with buckwheat, Fagopyrum esculentum) may also repel certain pests, but this is not as well documented. Apply the mulch before plants emerge from the soil and leave a narrow, mulch-free strip along the planting row. and an Udoll soil. A uniform decimal code for growth stages of crops and weeds. ; Lei, Z.R. Thrips are tiny insects that can damage plants. ; Wollkind, D.J. A&T State University. Calif. Agric. Feeding results in various tissue responses, including scar formation and distorted growth. Greenhouse thrips can infest many plant species but primarily is a pest of evergreen, broadleaved perennials. The differences in the monitored years were not confirmed, but the occurrence of the thrips varied depending on the time of sampling collection. *As of August 1, 2020, pesticides containing the active ingredient carbaryl are restricted use materials in California. Thrips hatch from eggs in a larval form and continue to mature. Biochim. NC State University and NC Cooperative Extension is based at North Carolina's two land-grant institutions, Publ. Trunk spray or injection of an effective, systemic, neonicotinoid insecticide can provide relatively rapid control. 2010 Oct;19(5):727-44. doi: 10.1007/s11248-009-9351-3. Lisowicz, F. The occurrence of economically important maize pests in south-eastern Poland. How to Get Rid of Thrips If you have. Thrips, order Thysanoptera, are tiny, slender insects with fringed wings. Cooperative Extension prohibits discrimination and harassment regardless of age, color, disability, family and marital status, gender identity, national origin, political beliefs, race, religion, sex (including pregnancy), sexual orientation and veteran status. determine how thrips infestations impact yield. Their presence was affected by the maize growth phase and growing seasons and partially by the weather. Please enable it to take advantage of the complete set of features! Stippling as result of greenhouse thrips feeding. ; Dedryvr, C.A. The first table below shows the 5-day DD60 forecast if you planted on April 16 or 17, 2023. To avoid tree injury and potential spread of pathogens on contaminated tools, use a soil application or trunk spray whenever possible, instead of injecting or implanting trees with insecticide. SOURCES:Missouri Botanical Garden: Thrips - indoors, Thrips - outdoors.UC IPM: Thrips.USDA-CSREES Integrated Pest Management Centers: Pest Thrips of the United States: Field Identification Guide.. Silvering is a result of the airspace left from dead cells. Thrips affect the flowers and the fruits of the eggplant which causes reduction in yield.The larvae and adult thrips feed and lay eggs on young leaves, flowers and on young fruits of many different plants and are the most serious pest in eggplant, sweet pepper, cucumber and bitter gourd. This mode of reproduction and rapid life cycle (dependent on temperature) allows them to build up in large numbers. Ges. Population dynamics of insect pests of cotton in Dera Ismail Khan. Cookies collect information about your preferences and your devices and are used to make the site work as you expect it to, to understand how you interact with the site, and to show advertisements that are targeted to your interests. ; Fail, J.; Shelton, A.M. Onion thrips (Thysanoptera: Thripidae): A global pest of increasing concern in Onion. Thrips began infesting the maize plants at the stage BBCH 1934 and ceased infesting plants in BBCH 69. Find support for a specific problem in the support section of our website. A global invasion by the thrips, Frankliniella occidentalis: Current virus vector status and its management. Thrips parasitized by this wasps larvae become swollen around the head and turn black, in contrast to the pale color of unparasitized greenhouse thrips larvae. permission is required to reuse all or part of the article published by MDPI, including figures and tables. https://doi.org/10.3390/toxins14070502, Subscribe to receive issue release notifications and newsletters from MDPI journals, You can make submissions to other journals. Avoid shearing plants, which is the clipping of dense foliage to maintain an even surface on formal hedges or creating specific shapes (topiary). But for homeowners, the better advice is to avoid synthetic chemicals altogether and rely on the other methods of integrated best management. ; Fuchs, F.; Nault, B.A. DVD ISBN 978-1-86499-940-2. Check with your local extension office for information about what species of these microscopic soil worms are effective against thrips in your area. ; Werren, J.L. Dominant Negative Mutants of Bacillus thuringiensis Cry1Ab Toxin Function as Anti-Toxins: Demonstration of the Role of Oligomerization in Toxicity. })(window,document,'script','dataLayer','GTM-NPR7B4'); And gardens with a lot of ground debris are likely to be thrip havens, as the eggs deposited in plant tissues can readily overwinter to hatch as nymphs the following spring. and transmitted securely. eCollection 2015. Yin, Y.; Xu, Y.; Cao, K.; Qin, Z.; Zhao, X.; Dong, X.; Shi, W. Impact assessment of Bt maize expressing the Cry1Ab and Cry2Ab protein simultaneously on non-target arthropods. Furthermore, insecticide seed treatment use in soybeans has driven resistance to seed treatments for tobacco thrips in cotton. They may develop high populations in cotton grown near corn and small grains such as wheat. 2016;60:8293. No special Multiple research trials have indicated that, although plants may look very poor, thrips do not need a foliar insecticide treatment. A new attractant for monitoring western flower thrips, Frankliniella occidentalis in protected crops. Large numbers of thrips in traps, or adults in flowers feeding on pollen, do not necessarily indicate that control action is needed. Find more information at the following NC State Extension websites: N.C. Most recyclers will not accept plastics with soil on them; therefore, plastic mulches typically are disposed of in landfills. To be effective, contact sprays must be applied to thoroughly cover buds, shoot tips, and other susceptible plant parts where thrips are present. Thrips damage can result in scars on leaf, flower, and fruit surfaces and distortion of plant parts. We found that MON810 maize had no effect on the occurrence or composition of thrips. Conversely, when a greenhouse thrips emerges from an unparasitized egg, part of the egg shell is often visible at the side of the egg blister. The effect of thrips is highly influenced by crop health. Bethke, J. The decrease in thrips populations in our study was most likely caused by pollen shedding and climatic conditions. 4 mango disorders that can affect yields. Our research contributed to scientific knowledge of thrips communities found on maize plants in Central Europe, including Bt maize. Biology and ecology of the western flower thrips (Thysanoptera: Thripidae): The making of a pest. Application of Ultra-high Performance Liquid Chromatography-Mass Spectrometry (UHPLC-MS) Metabolomic Fingerprinting to Characterise GM and Conventional Maize Varieties. Impacts of developing on Bt maize-intoxicated hosts on fitness parameters of a stemborer parasitoid. Where the roots of nearby plants grow near treated plants, those other plants may also take up some of the soil-applied insecticide. 'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f); Fortunately, most thrips are susceptible to some of the same controls, such as exclusion and certain insecticides. Our obtained data also provide information about the thrips species representations typical for the cereals, represented on Bt and non-Bt maize plants and their seasonal dynamics which can be useful for future planning of maize integrated plant protection in Central Europe if thrips started to be a serious pest of maize. Where thrips are a problem, learn whether that pest has specific natural enemies important in its control. You can find out more about our use, change your default settings, and withdraw your consent at any time with effect for the future by visiting Cookies Settings, which can also be found in the footer of the site. Thrips feeding is usually accompanied by black varnishlike flecks of frass (excrement). Thrips. Myoporum thrips can create tightly bunched and twisted terminal growth that resembles a gall, within which large numbers of thrips can survive and reproduce. Before long, widespread infestation halts the growth of your weed, significantly diminishes yield size, and can spell the end for your pot. Commercially available synthetics include aluminum-metalized polyethylene and silver-embossed polyethylene plastic films. They weaken the outer shell of thrips but are safe to use on your plants and they don't leave much of a residue. Smart Grocery Shopping When You Have Diabetes, Surprising Things You Didn't Know About Dogs and Cats. PMC Citrus thrips and western flower thrips are also found in avocado but do not damage avocados. With soaps, coverage is very important as it does not stay on your plant for long, so follow-up applications may be necessary. Thrips are wide-spread piercing-sucking insects which are responsible for severe yield reduction in vegetable crops such as cucumber, strawberry, melon and pepper ( Shipp et al., 2000; Park et al., 2007; Peng et al., 2011; Sampson and Kirk, 2013 ). In total, 3426 thrips were caught. Res. Herbicide Wing P (4.0 L/ha) was applied after sowing on 7 May. Annually, 180 (2013, 2014) and 160 (2015) traps were used. ----- Thrips (various species) Symptoms: Thrips are small (1 mm long), brown or black insects with a tapering, segmented abdomen. Symptoms. Thrips feed on plant or fungal tissue by piercing the outer layer of the organism and sucking out the contents of the affected cells. commitment to diversity. Reitz, S.R. ; Smith, H.A. Not all species are considered pests. 311332. https://doi.org/10.3390/toxins14070502, Cag, udovt, Peter Bokor, and Oxana Skokov Habutov. Thrips, T. tabaci, and the bulb mites, Aceria tulipae and Rhizoglyphus spp., affect stored onions and garlic. ; Kucharczyk, H.; Grski, D. Effects of Insecticides Used against the European Corn Borer on Thrips Abundance on Maize. The first sign of thrips is usually yellow or bleached spots on leaves, deformed leaves, or dead blotches on flower petals. In many thrips species, by the time their damage is observed, such as after buds open, the thrips may no longer be present. Oakland: Univ. ; Klein, H.; Dutton, A.; Bigler, F. Effects of Bt maize on Frankliniella tenuicornisand exposure of thrips predators to prey-mediated Bt toxin. If injecting or implanting multiple trees, prevent the potential spread of pathogens on contaminated tools; before moving to work on each new tree, scrub any plant sap from tools or equipment that penetrate trees and disinfect them with a registered disinfectant (e.g., bleach). Drip or furrow irrigation is generally necessary when using row covers. Next Article in Journal ; Reitz, S.R. government site. But if the plant damage is due to thrips, the leaves will nearly always show the black spots created by the pest's excrement. Many studies have reported that higher bulb yields were obtained with insecticides that reduced the density of thrips (Gachu et al. While thrips have mouthparts adapted for piercing and sucking plant juices, they are too small to pierce the skin and are not inclined to bite humans, as they are not blood feeders. However, thrips reduction is not necessarily translated in yield increase. [, Bergant, K.; Trdan, S.; nidari, D.; repinek, Z.; Kajfe-Bogataj, L. Impact of Climate Change on Developmental Dynamics of. The maize grain was collected using a CLASS LEXION 600 harvester with an adjustable row adapter. those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). Another way to encourage natural predators is through the careful, restricted use of pesticides. Predatory thrips can sometimes be distinguished from pest species because predators are seldom seen at high levels as can be common with certain pest thrips. The authors declare no conflict of interest. ; Griset, J.G. We confirmed the significant influence of the experimental seasons on maize grain yield between the monitored years 2013 and 2014, 2013 and 2015, and 2014 and 2015. When used for thrips, a good method is to combine four teaspoons neem oil, two teaspoons of white dishwashing liquid, and one gallon of water. Smith, E.A. Among the flowering plants, gladiolas, carnations, chrysanthemums, gerberas, marigolds, pansies, hibiscus, and any of the plants from the rose family, are common targets. Read our ; Wood, M.; Butt, T.M. Svobodov, Z.; Skokov Habutov, O.; Hutchison, W.D. This is consistent with another study in which thrips, Bt crops have a narrow spectrum of activity, they have no negative effects on non-target organisms [, Linear approximation for this function may result in underdevelopment at low temperatures and overdevelopment at high temperatures. Before taking control action, look carefully for the insects themselves to be certain that pest thrips are present and the cause of the damage. The findings on thrips communities on maize plants, including Bt maize, in Slovakia, will add to scientific knowledge in Central Europe and could be used for future research. ; Munkvold, G.P. Eventually, the leaves and petals will become deformed, or become thin and wilted, thendie and drop off. and O.S.H. Aluminum foil is also effective and may be suitable for a small garden; but it is expensive and difficult to reuse because it is delicate to handle. Covering important plants with fine mesh screening may prevent infestations. 2017 Feb 1;110(1):221-229. doi: 10.1093/jee/tow276. A Feature Resende D.C., Mendes S.M., Marucci R.C., Silva A.C., Campanha M.M., Waquil J.M. Accessibility Ramakers, Applied Plant Research , Bugwood.org. MV Madhusudhan, deputy director of Telangana's horticulture department, agrees that the pest attack has substantially reduced the yield of chilli this year from the usual 5-6 tonnes per ha to 2.5 tonnes or less. Paper should be a substantial original Article that involves several techniques or approaches, provides an outlook for You are accessing a machine-readable page. Improper timing of application, failure to treat the proper plant parts, and inadequate spray coverage when using contact materials are common mistakes that can prevent potentially effective insecticides from actually providing control. However, thrips can transfer plant-specific viruses between plants. The biology and ecology of onion thrips, Thrips tabaci Lindeman, and current management strategies based on chemical, biological, and cultural control as well as host resistance are discussed. Changes in weather conditions are presented from June to October to cover the entire monitoring period (. Czech J. Due to rising temperatures and precipitation, as well as frequent wind gusts, the thrips on maize plants decreased in the first and second part of August (BBCH 6973, end of floweringmilk stage of grain) (, Climate conditions factors observed before and after sample collection using the Pearson correlation coefficient were not confirmed significantly (, The year 2014 was the second year of monitoring with the same number of sticky traps installed as in the previous year. 2008. Res. Lisowicz, F. Theoretical and practical bases for applications of integrated pest control protecting corn from damages. Bernal, J.S. Furthermore, across extensive multi-year extension research trials, yields have never been show to benefit from any insecticidal seed treatment. Families: 1 Aeolothripidae; 2 Phlaeothripidae; 3 Thripidae. Unlike healthy black mature thrips, the black parasitized larvae are smaller and do not move. Amanda Rose Newton holds degrees in Horticulture, Biochemistry, Entomology, and soon a PhD in STEM Education. Graham, S.H. Leaves of affected plants yellow, wither, deform . Prune by cutting plants just above branch crotches and nodes instead of shearing off terminals. Cropping system influences Tomato spotted wilt virus disease development, thrips population and yield of tomato (. This pest has also been associated with the transmission of viral diseases in potato fields (Marchoux et al., 1991; Jones, 2005). Insecticidal soaps work well to control thrip infestations. Citrus thrips feeding severely distorts blueberry shoot tips and foliage, reducing fruit yield. doi: 10.1016/j.toxicon.2006.11.022. Damage is usually fairly moderate, though large numbers of thrips can kill a plant. Disclaimer. (N)-number of specimens; % percentage share. Infested terminals may discolor and become rolled. A variety of natural predators will devour thrips and their eggsin fact, these predatory insects are so efficient that they are often purchased and introduced deliberately by commercial growers and greenhouse operators. An official website of the United States government. Thrips can affect hundreds of different ornamental and edible plants, and they are extremely resistant to eradication. This is especially helpful for gladiola bulbs, which are notorious for harboring thrips. For You can try a combination of chemical and natural treatments to remove and prevent infections of thrips. The trials for the Bt and isogenic plots were completely random. Do not implant or inject roots or trunks more than once a year. And chemical pesticides are very likely to kill the predatory insects that are most helpful for controlling thrips. They also leave behind traces of their feces, which look like black spots on the leaf. Citrus thrips occur on many species of plants but damage only blueberries and citrus. We found that MON810 maize had no effect on the occurrence or composition of thrips. Publ. Please note that many of the page functionalities won't work as expected without javascript enabled. Mitt. 2013 . Entomol. In addition, thrips can spread diseases between plants. Early detection andintegrated pest management(IPM) are the best options for preventing a wide-ranging infestation. Harrington, R.; Fleming, R.; Woiwod, I. J Econ Entomol. If management is necessary, use an integrated program that combines the use of good cultural practices, natural enemies, and the most selective or least-toxic insecticides that are effective in that situation. Late in the same growing season, however, the nitrate level was 3.2-fold greater . For example, myoporum thrips causes severe galling of Myoporum laetum and M. pacificum. Genetically engineered crops help support conservation biological control. Thrips (thysanoptera) are a common, widespread pest that affect a variety of host. articles published under an open access Creative Common CC BY license, any part of the article may be reused without Cag, L.; Praslika, J.; Huszr, J.; robrov, A.; Rohik, T.; Hudec, K.; Tancik, J.; Bokor, P.; Tth, P.; Tthov, M.; et al. The direct effect on the grain yield was not confirmed. Synthetic mulch application methods include: In addition to temporarily repelling certain flying insects, mulch may improve growth of certain crops by increasing light levels, keeping soil warmer overnight, reducing weed growth, and conserving soil moisture. Khan, S.M. Muz-Garay, C.; Portugal, L.; Padro-Lpez, L.; Jimenz-Jurez, N.; Arenas, I.; Gmez, I.; Snchez-Lpez, R.; Arroyo, R.; Holzenburg, A.; Sawa, C.G. U.S. STD Cases Increased During COVIDs 2nd Year, Have IBD and Insomnia? Pyrethrin is a natural pesticide derived from the flowers of certain types of chrysanthemum flowers. There are more than 7,000 varieties of thrips around the world. Reproductive modes in onion thrips (Thysanoptera: Thripidae) population from New York onion fields. Lay lightweight material that allows light and air penetration over the top of a crop that is sturdy enough to lift the material as it grows. Before The Bt-transgenic toxin Cry51Aa2.834_16 is expected to reduce the need for insecticide applications targeting thrips and tarnished plant bug and could be a valuable addition to an overall insect management program in cotton. In order to be human-readable, please install an RSS reader. ; Scott, M.A. The species included. 2001. Produced by University of California Statewide IPM Program. Small silver patches are seen on the upper side of leaf blades, an effect known as 'silvering'. For example, if you spray with a pesticide carrying the 3A IRAC code (which identifies it as a pyrethroid pesticide), you should shift to a different code for the next spraying. Bras. Where thrips lay eggs on grapes, fruit may develop dark scars surrounded by lighter halos. Thrips feeding on apples, nectarines, and raspberries can deform or scar developing fruit. Petzold-Maxwell JL, Jaronski ST, Clifton EH, Dunbar MW, Jackson MA, Gassmann AJ. The thrips species, The last most abundant collection appears at the end of July (BBCH 65-female: stigmata tips visible, male: upper and lower parts of tassel in flower), with, In August (BBCH 6973, end of floweringmilk stage of grain), thrips numbers decreased with the exception of a few isolated pieces. From three years of monitoring, 3426 individuals were confirmed in the traps, with 1705 on non-Bt and 1721 on Bt maize. Svobodov Z, Skokov Habutov O, Hutchison WD, Hussein HM, Sehnal F. PLoS One. These materials are highly toxic to natural enemies and pollinators, can cause spider mite outbreaks, and are not particularly effective against most thrips. In, Resende, D.C.; Mendes, S.M. This study was supported by the Operational Program Integrated Infrastructure within the project Sustainable smart farming systems taking into account the future challenges (ITMS 313011W112), co-financed by the European Regional Development Fund. Many different species of thrips occur on soybeans. Despite their small size, these insects have the potential to cause yield reductions of more than 100 pounds of lint per acre; extremely heavy infestations can even cause death of seedling plants. Mulch or mesh that reflects light interferes with certain flying insects ability to locate plants. They will not cause a yield loss and no treatment is needed. A 5 m wide strip of barley separated each plot from the others. USDA-CSREES Regional Integrated Pest Management Centers (PDF). Furthermore, maize grain yield, abundance, and seasonal dynamics of the followed thrips on plants were not affected by the type of maize grown (Bt versus non-Bt) but were affected by the growing season. The presence of thrips over the three years of monitoring was related to maize yields and the effect on the maze yield was evaluated. Old, spent flowers can harbor thrips, so their removal and disposal is sometimes recommended. Entomol. The experimental area was fertilized in 2014 with the same preparations as the previous year, but with a different N dose (100 kg/ha: N46%). Environmental Science and Pollution Research. A&T State University, in all 100 counties and with the Eastern Band of Cherokee PDF reader. Learn tips for creating your most beautiful home and garden ever. In three years, we observed an increase in thrips population at the start of the vegetation period, and the peak of thrips population on maize occurred similarly on 15 July, 8 July and 16 July 20132015. Assess whether spraying is warranted and select materials that are least toxic to natural enemies. J Econ Entomol. Thripobius semiluteus parasitizes greenhouse thrips larvae. Cuban laurel thrips create tightly rolled, podlike leaf terminals on Ficus and form galled foliage from midsummer through fall. ; Carneiro, A.A.; Valicente, F.H. Parsons, M.W. ; Wu, S.Y. FOR ALL OTHER USES or more information, read Legal Notices. The direct effect on the grain yield was not confirmed. In total 520 transparent sticky traps were analyzed for the presence of thrips depending on the physiological growth stage of maize. These insects are very small (less than 1/10 inch) and are torpedo shaped. Federal government websites often end in .gov or .mil. All rights reserved. Spinosad (Captain Jacks Deadbug Brew, Green Light Lawn & Garden Spray with Spinosad 2, Monterey Garden Insect Spray) is generally more effective against thrips than the products above. ; Khan, M.A.U. These pesticides are usually not very effective, because of the way thrips feed and reproduce. Division of Agriculture and Natural Resources CABI is a member of: The Association of . Obrist, L.B. For more information see the California Department of Pesticide Regulation website. However, thrips can be positively identified to species only by an expert. Because there are so many different types of thrips, most indoor and outdoor plants, both woody and herbaceous, can be affected by them. Harris, H.M.; Drake, C.J. Ph.D. Thesis, Swedish University of Agricultural Sciences, Uppsala, Sweden, 2005; 42p.