1 Research Geneticist. 2 Research Plant Pathologist. We acknowledge the assistance of Agricultural Research Technicians F.P. Maguire and M.M. Hulsey. This work was supported in part by the Integrated Pest Management Collaborative Research
Integrated Pest Management Collaborative Support Program (IPM CRSP), U.S. Agency for International Development (USAID), under Grant No. LAG-4196-G-00-3053-00. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal
1 Research geneticist. 2 Research plant pathologist. This work was supported, in part, by the Integrated Pest Management Collaborative Support Program (IPM CRSP), U.S. Agency for International Development (USAID), under Grant Numbers LAG-4196-G-00
research was partially supported by funding from the North Central Region Integrated Pest Management Program. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the Univ. of Illinois or the
1 Research genetieist. 2 Research plant pathologist. The technical assistance of F.P. Maguire, M.M. Hulsey, and E.L. Corley, Jr., is gratefully acknowledged. This work was supported, in part, by the Integrated Pest Management Collaborative Research
This research details the influence of fertility on plant growth, photosynthesis, ethylene evolution and herbivore abundance of chrysanthemum (Dendranthema grandiflora Tzvelev `Charm') inoculated with cotton aphids (Aphis gossypii Glover). We tested five fertility levels that consisted of 0%, 5%, 10%, 20%, and 100% (375 ppm N) of recommended nitrogen levels. Aphid abundance was greatest at high fertility. Fertility affected the vertical distribution of aphids. A higher population of aphids were observed in physiologically mature and older leaves at low fertility, whereas at high fertility young leaves had 33% more aphids than older, basal leaves. Aphids depressed plant vegetative and reproductive growth, and altered carbohydrate partitioning at high fertility. Aphid-inoculated (AI) plants at high fertility had increased specific leaf area [(SLA), i.e., thinner leaves] and greater leaf area than aphid-free (NonAI) plants. Aphids caused greater ethylene production in reproductive buds and young leaves of high fertility plants, but had no effect on ethylene evolution in physiologically mature or older, basal leaves. Plant growth, leaf nitrogen (N), phosphorus (P), iron (Fe) and manganese (Mn) increased at higher fertility, as did chlorophyll and photosynthetic rates. Leaf N was highest in young and physiologically mature leaves compared to basal leaves. Aphids decreased leaf N and P. Aphids reduced photosynthesis in young leaves of high fertility plants, whereas physiologically mature and older leaves were unaffected.
The effects of overhead and drip tube irrigation on twospotted spider mite (TSMs) (Tetranychus urticae Koch) and predatory mite (PMs) (Phytoseiulus persimilis Athias-Henriot) populations, as well as the biological control of TSMs by PMs, were investigated on Impatiens wallerana Hook. f. `Impulse Orange'. To determine the effects of the two irrigation methods on TSM populations, plants were inoculated with female TSMs 6 weeks after seeding. Plants were then irrigated twice every three days, and TSM counts were taken 3 weeks later. To assess the effects of irrigation method on PMs, plants were inoculated with TSMs 6 weeks after seeding, PMs were released 10 days later, plants were irrigated about once per day, and the number of predatory mites on plants was counted 3 weeks after release. To assess the effects of irrigation method on the biological control of TSMs by PMs, plants were inoculated with TSMs and PMs were released as before, but then plants were irrigated either three times every 2 days or three times every 4 days using either drip or overhead irrigation. The number of TSMs on plants and the number of leaves showing TSM feeding injury were measured 3 weeks after predator release. Overhead watering significantly reduced TSM and PM populations as much as 68- and 1538-fold, respectively, compared to drip irrigation with microtubes. Perhaps more important, overhead watering with or without predators significantly reduced the number of leaves sustaining TSM feeding injury as much as 4-fold compared to drip irrigation. These results confirm the common observation that TSM infestations and injury may be reduced by irrigation systems that wet plant foliage. However, predators still reduced TSMs even though overhead irrigation had a suppressive effect on predatory mites. Predators are particularly useful for reducing TSM injury when plants are watered infrequently. Overhead watering could be used in tandem with biological control as a component of an integrated crop management program for TSMs in ornamental greenhouses by rapidly lowering TSM population levels in hot spots before PMs are released.
The hypothesis was tested that effects of late-season European Red Mite (ERM) [Panonychus ulmi (Koch)] injury on apple (Malus domestica Borkh.) fruit development are better explained by carbon physiology than by pest densities. Midseason ERM populations were allowed to develop in mature semi-dwarf `Starkrimson Delicious'/M26 trees with moderately heavy crops, then were controlled with miticides at different mite-day (activity of one mite per leaf for 1 day) levels as estimated by weekly leaf sampling. The range of final mite-days was from 250 to 2100 on individual trees. Seasonal fruit growth patterns were monitored. Diurnal whole-canopy net CO2 exchange rate (NCER) was measured in eight clear flexible balloon whole-canopy chambers on several dates before and after mite infestations. Mite injury reduced fruit growth rates. Leaf and whole-canopy NCER were reduced similarly. Late season fruit growth and final fruit size were correlated with accumulated mite-days, but were better correlated to whole-canopy NCER per fruit. Fruit firmness, color, soluble solids and starch ratings showed no correlation to mite-days. Number of flower clusters per tree and final fruit per tree the following year were not related to accumulated mite-days, but final fruit per tree the following year were better correlated to whole-canopy NCER per fruit. These results generally supported the hypothesis.
Fruit maturity, quality, calcium concentration and economic value of `Starkrimson Delicious' (Malus domestica Borkh.) apples, under a range of crop levels and European red mite [Panonychus ulmi (Koch)] cumulative mite-days (CMD), were best explained by local surface regression models involving CMD and crop load. Fruit from trees with low CMD and a light crop (125 fruit/tree, about 20 t/ha) were the most mature at harvest. Those fruit had higher ethylene concentrations, starch pattern indices, soluble solids concentrations, and watercore incidence at harvest than fruit from trees with low CMD and a normal crop (300 fruit/tree, about 40 t/ha), or with high CMD at any crop level. Those fruit also had higher incidences of watercore and internal breakdown after 4 months of cold storage. Calcium concentrations in fruit increased as crop load and CMD increased. Whole-canopy net CO2 exchange rate per fruit related better to fruit quality and calcium concentrations than either crop load or CMD alone, but was always a much worse predictor than local surface regressions. Low CMD and normally cropped trees had the highest crop value; lightly cropped trees had an intermediate crop value; while high CMD and normally cropped trees had the lowest crop economic value. Crop load should be considered when defining action thresholds for mites, and harvest schedules for apples should reflect crop load and mite populations on apple trees.
Collard greens (Brassica oleracea var. acephala L.) were planted in the peripheries of cabbage (Brassica oleracea var. capitata L.) fields in the spring growing seasons of 1997 and 1998 to evaluate their effectiveness as a trap crop to manage the diamondback moth (DBM) [Plutella xylostella (L.)]. The numbers of DBM never exceeded the action threshold for application of insecticides in any of the fields that were completely surrounded by collards, but did exceed the action threshold in three of the fields without collards on four sampling dates in 1998. In both years, the numbers of DBM larvae in the collards exceeded the action threshold of 0.3 total larvae/plant in eight of nine fields. Larval counts in cabbage surrounded with collards were not significantly higher than in the conventionally planted cabbage, even though the number of pesticide applications was reduced in the former. The few pesticide applications in fields surrounded by collards probably targeted the cabbage looper [Trichoplusia ni (Hübner)], which was not impeded by the collards from infesting the interior cabbage. There was no significant reduction in marketability, and damage to cabbage was similar to that in fields where collards were planted and in fields where only conventional pesticides were used. The reduced number of pesticide sprays, as well as the high concentration of host larvae in the collards, may help maintain populations of natural enemies of DBM in the agroecosystem. Planting collards in field peripheries is a potentially effective tactic to manage DBM in cabbage.