Microbial biomass varied as a result of both the cover-crop and weed control treatments. In both the middles and vine rows, microbial biomass was higher in rye cover-crop plots compared to bare plots . These results confirm earlier observations by Ingels et al. that microbial biomass carbon was higher in cover-cropped middles compared to bare middles. In the vine rows, microbial biomass was greater in plots adjacent to rye cover-cropped plots compared to bare plots. The effect of cover crops grown in the middles on soil in the vine rows may be due to cover-crop roots or tops extending into the vine rows and their subsequent decomposition, providing a food source for soil microbes. Microbial biomass varied between the weed treatments in the vine rows but not middles . In the vine rows, microbial biomass was significantly higher in the cultivation plots compared to the pre-emergence weed control plots . The most likely explanation is the incorporation of greater amounts of weed-derived carbon into the surface soil of the cultivated plots. Mycorrhizae. AMF can benefit grapevines by improving the nutritional 35 30 25 20 15 10 5 0 Cultivation Post-emergence Pre-emergence herbicide herbicide Bare ground Merced rye Trios 102 status of the plant and producing a highly branched root system. We quantified AMF reproductive structures in grapevine roots to determine if the weed control treatments in the rows and/or cover-crop treatments in the middles had significant effects on mycorrhizal colonization from 2003 through 2005.
Based on ANOVA, the effects of weed control on colonization were not consistent among covercrop treatments . Grapevines adjacent to ‘Merced’ rye had higher colonization compared to those adjacent to ‘Trios 102’ triticale or bare ground, in both the cultivation and pre-emergence treatments . In contrast,drainage gutter grapevines in the post emergence treatment had the lowest colonization when adjacent to ‘Merced’ rye. These findings were consistent in each study year, based on the absence of significant main or interactive effects of time . It is possible that low colonization of grapevines in the post-emergence-by-‘Merced’ rye treatment is associated with this treatment’s weed community. Indeed, weed species vary in their ability to host AMF , so their presence or absence may affect mycorrhizal colonization of grapevines. Indeed, reports on the influence of plant community composition on AMF suggest that plant diversity has a strong effect on AMF diversity , and this may affect the colonization of individual plant species. All yield, fruit quality and vine growth parameters varied by year, and this was the only significant effect for these parameters, with the exception of berry weight and titratable acidity . No differences in crop yield or fruit composition were observed from 2001 to 2005 due to weed control treatments . Cover-crop treatments also had no significant effect on yield or fruit composition, although in 2001 and 2004, there was a reduction in berry size in the ‘Trios 102’ triticale treatment. Weed control treatments also had no effect on vine growth , based on shoot counts and pruning weights taken at dormancy. Cover-crop treatments had no significant effect on vine growth when averaged over 5 years, although in 2001 and 2005 the ‘Trios 102’ triticale treatment significantly reduced pruning weights.
The trend for lower pruning weights may be related to the greater decline in soil moisture in the middles where this cover crop was used. It appears that vine growth, yield and grape quality are more significantly affected by annual precipitation than by vineyard floor management practices. In low rainfall areas the choice of cover crop is critical because of its effect on available soil moisture. We observed that late-maturing ‘Trios 102’ used more soil moisture during the vine growing season; if irrigation water does not compensate for water used by the cover crop, reduced vine growth and yield losses may result. The clear benefits of cover crops were increased organic matter in the middles and reduced sediment loss. Microbial biomass was increased in cover-cropped middles and there were indications that this effect extended to under the vines. Although there were no negative impacts of weed control treatments on vine productivity, we observed increased compaction over time from the use of cultivation. This study indicated that the choice of weed control strategy and cover crop must be carefully considered to maximize the benefits and minimize negative impacts of the practices. The benefits of cover crops are concentrated in the middles, and future research should focus on evaluating practices that improve the quality of soil under the vines.Thrips are members of the order Thysanoptera. This order is subdivided into two suborders, the Terebrantia and the Tubulifera, with about 5,500 described species in nine families . The Terebrantia consist of seven families, six of which are present in North America.
All members of the Terebrantia have the following in common: the last abdominal segment is rounded or conical, females possess an ovipositor, forewings have veins and setae, fringed cilia of the forewing arise from the basal sockets, and the wing surface typically has numerous microtrichia . The Tubulifera consist of two families, but only one of them is present in North America . The Tubulifera may be distinguished from the Terebrantia by the following characteristics: both males and females have a tubular last abdominal segment, females lack an ovipositor, forewings lack veins and setae except at the base, the fringe cilia lack basal sockets, and the wing surface is bare of microtrichia . The families within the Terebrantia are separated by antennal characters, mainly the number of segments and type of sensoria on the third and fourth segments . Thrips are tiny, slender, and soft-bodied insects that are 0.5 to 5.0 mm in length. When wings are present, there are four very long and narrow wings that are fringed with long hairs. This fringe, or tassel, gives the order its name, thysano, the Greek word for tassel and ptera meaning wing. The mouthparts of thrips are unusual and of the sucking/piercing type. There are two principle structures. The first structure consists of the left mandible, which is modified into a tough, sharp, piercing organ that is hollow but lacking an aperture; the right mandible is reduced and vestigial . The second structure is composed of the paired styliform lacineae of the maxillae, which are interlocked to form a single feeding tube . These structures are contained inside the proboscis that is located opistignagthically on the ventral surface of the head. The labrum forms the front of the proboscis; the basal portions of the maxillae form the sides and the labium forms the rear . Thrips also exhibit unique metamorphosis, being neither truly hemimetabolous nor holometabolous. The first two instars have no external wings, are referred to as larvae, and are mobile but are relatively slow moving. In many cases, the wings develop internally during these two instars . In the Terebrantia, the third and fourth instars are inactive, unless disturbed, non-feeding, and some lack external wings. The third and fourth instars are referred to as the propupa, and pupa respectively, though they are not ‘true pupae’ and they are followed by the adult stage. Thrips in the suborder Tubulifera have two pupal stages following the propupal stage. Thrips range in color from translucent white or yellowish to dark brown or blackish depending on the species and life stage . The sexes of thrips are similar in appearance, though the male is often smaller and moves faster than the female. Parthenogenesis can occur in many species of thrips . When an ovipositor is present, phytophagous females ususally oviposit into plant tissue . The eggs are typically oviposited under the cuticle of new leaves, stems and fruit where the larvae feed. In many species,plastic gutter one female may lay as many as 250 eggs. The late second instar of many species drop to the soil or leaf litter or lodge within plant crevices to pupate. However, greenhouse thrips pupate openly on lower leaf surfaces while pupae and eggs of some gall-forming species occur on leaf surfaces but are enclosed within distorted plant tissues. Thrips have several generations per year, some having 8 or more. In some species, the life cycle from egg to adult may be completed in as short as two weeks when environmental conditions are optimal. Nearly 50% of the known species of thrips feed on fungi, about 40% feed on living tissues of dicotyledonous plants or grasses, and the rest exploit mosses, ferns, gymnosperms, and cycads or are predatory . Phytophagous thrips mainly feed upon the rapidly growing foliage or ‘flush’ as well as very small, developing fruits typically not larger than 5 cm in diameter.
Because of the preference of thrips for immature fruit and flush foliage, external injury to commercial fruit and plants may be difficult to detect in the early stages of growth. Thrips feeding causes tiny scars on leaves and fruit, often referred to as stippling. Stippled leaves become distorted, colored, rolled, stunted and are often abscised by the plant. Avocado, citrus and greenhouse thrips cause silver to brown scabby scars on avocado and citrus fruit surfaces, but the damage is usually cosmetic . Evidence of thrips damage on grapes appears as dark scars surrounded by lighter colored ‘halos’ . Thrips damage may cause apples, nectarines, onion, pears, soybean, sugar pea pods, raspberries and tomato, to be deformed, scarred and scabbed . Some thrips detrimental to crops of economic importance feed on and over-winter in weed hosts and plant material left in growing fields and presumably move into crops when environmental conditions are appropriate . Like many insects with incomplete metamorphosis, thrips adults and larvae compete for the same food resources. Phytophagous species are often broadly polyphagous, attacking a wide range of host plants representing a spectrum of agricultural crops and non-crop species. For example, western flower thrips, Frankliniella occidentalis , is an important and polyphagous greenhouse and field pest with vegetables and ornamental crops being the most important host plants. Western flower thrips cause direct damage on the plants and indirect damage as a vector of tomato spotted wilt and other viruses . It infects a wide range of crop and non-crop hosts and causes economic losses worldwide that are estimated at $1 billion per year . Thrips tabaci Lindeman is an important pest of sweet peppers and also vectors a tospovirus . The melon thrips, Thrips palmi Karny, is a pest of over 60 economically important crops and bean thrips, Caliothrips fasciatus , is a pest of over 60 plant genera andapproximately 30 economically important crops, although this number may be an overestimation . Because thrips populations can build up to injurious levels very quickly if left unchecked in native habitats and in crops where flush is present, colored sticky cards are often used to monitor for thrips levels . Other monitoring methods include visual inspection, a turpentine funnel wash, and shaking, sweep-net, or beat tray sampling . Visual inspection and sweep-netting can give some indication as to the presence of thrips, while beating or shaking the plant material and collecting the insects is also sufficient but more labor intensive with extraction efficiency being low. Because thrips can rapidly increase in numbers and move from field to field, it is often necessary to sample thrips frequently. Many thrips species are key pests of economically important crops and ornamentals, including avocado, citrus, cotton, cowpea, melon, onion, pecan, rose, strawberry and many ornamental flowers . Historically, chemical controls have been used to combat these pests. The insecticides imidacloprid , abamectin , methomyl , spinosad , spinetoram and endosulfan include only a few of the many insecticides that have been or are currently used to chemically control thrips species . However, management of thrips with insecticides can be difficult, especially when they invade fields and crops when flush is present, which can be at multiple points during the year depending upon the crop. In addition, repeat sprays are often required as thrips populations continue to emigrate into crops from nearby plants in native habitats or other crops. Also, the egg and pupal stages of thrips are often protected from spray impact. The utility of chemical control can change rapidly because of resistance development, environmental contamination, non-target effects on beneficial insects and increased public awareness and concerns, resulting in restrictions or near elimination of several classes of insecticides.