James D. Dutcher

Warm-Season Cover Crops for Pecan Orchards: Horticultural and Entomological Implications

ABSTRACT In an experimental grove of pecan (Carya illinoinensis [Wangenheim] K. Koch [Juglandaceae]), we surveyed potential “insectary crops” that might provide aphidophagous insects and other entomophaga with alternate foods, and thereby enhance biological pest control. Thirteen prospective warm-season cover crops were evaluated for associated aphids and entomophagous insects; an additional 11 crops or mixtures were considered in unreplicated plots. Seven crops developed adequate stands in the replicated study: sericea lespedeza (Lespedeza cuneate [Dumont] G. Don, cultivar ‘Lowtan’, Fabaceae), American jointvetch (Aeschynomene americana L., Fabaceae), sesbania (Sesbania exaltata [Rafinesque-Schmaltz] Cory, Fabaceae), cowpea (Vigna unguiculata ssp. unguiculata [L.] Walpers, no named cultivar, but termed “combine” or “reseeding” cowpea, Fabaceae), alyceclover (Alysicarpus vaginalis[L.] De Candolle, Fabaceae), a sorghum X Sudan grass hybrid (Sorghum bicolor [L.] Moench cultivar ‘Kow Kandy’, Poaceae), and bu...

A Review of Resurgence and Replacement Causing Pest Outbreaks in IPM

Insect and mite pest resurgence occurs when an insecticide or acaricide treatment destroys the pest population and kills, repels, irritates or otherwise deters the natural enemies of the pest. The residual activity of the insecticide then expires and the pest population is able to increase more rapidly and to a higher abundance when natural enemies are absent or in low abundance. Replacement of a primary pest with a secondary pest occurs when an insecticide or acaricide treatment controls the primary pest and also destroys natural enemies of an injurious insect or mite that was regulated below an economic injury level by the natural enemies, thus, elevating the secondary pest to primary pest status. Disruption of natural controls is not always the cause of resurgence or replacement events. A dose-response phenomenon called hormesis can occur in pest populations exposed to sublethal doses of pesticides. This can cause an increase in fecundity (physiological hormoligosis) or oviposition behaviour (behavioural hormoligosis of the pest leading to a significant increase in its abundance. Selective insecticides and acaricides coupled with natural enemies and host plant resistance have become the alternative methods more commonly used by growers that encounter these problems. The purpose of this chapter is to review pesticide-induced resurgence and replacement in modern cropping systems and methods for measuring and resolving these problems.

Cool-season cover crops in the pecan orchard understory: Effects on coccinellidae (Coleoptera) and pecan aphids (Homoptera: Aphididae)

Abstract In mature pecan orchards under minimal or commercial management, cool-season understory cover crops of hairy vetch, Vicia villosa Roth, and rye, Secale cereale (L.), sustained significantly higher densities of aphidophagous lady beetles than did unmown resident vegetation or mowed grasses and weeds. In cover-cropped understories, mean densities of aphidophagous coccinellids were nearly 6 times greater than in unmown resident vegetation and approximately 87 times greater than in mown grasses and weeds. During late winter and spring, rye harbored abundant bird cherryoat aphid, Rhopalosiphum padi L., whereas hairy vetch sustained pea aphid, Acyrthosiphon pisum (Harris); blue alfalfa aphid, A. kondoi Shinji ; and thrips, Frankliniella spp. The following aphidophagous lady beetles were abundant in cover-cropped understories: (1) convergent lady beetle, Hippodamia convergens GuerinMeneville; (2) Olla v-nigrum (Mulsant); and (3) seven-spotted lady beetle, Coccinella septempunctata L. In the orchard under minimal management, there was evidence that the rye/vetch mixture led to enhanced densities of convergent lady beetle in the pecan trees. However, no other effects on coccinellids were seen. There was no evidence of improved biological control of pecan aphids

Synthetic 3,5-Dimethyldodecanoic Acid Serves as a General Attractant for Multiple Species of Prionus (Coleoptera: Cerambycidae)

ABSTRACT Males of the longhorned beetle Prionus californicus Motschulsky (Coleoptera: Cerambycidae) are significantly attracted to the female-produced sex pheromone (3R,5S)-3,5-dimethyldodecanoic acid. Males respond equally well to the synthetic blend of the four stereoisomers of 3,5-dimethyldodecanoic acid as to the single natural enantiomer, suggesting that the unnatural isomers are not inhibitory. Males of the congener Prionus lecontei Lameere also are attracted to the (3R,5S)-enantiomer but not to the (3S,5R)-enantiomer, suggesting that the (3R,5S)-enantiomer is also an important pheromone component of that species. Here, we report the results of field trials that test the hypothesis that synthetic 3,5-dimethyldodecanoic acid will serve as a general attractant for males of other Prionus species. We conducted field bioassays of synthetic 3,5-dimethyldodecanoic acid at study sites in six different regions of North America and one site in the United Kingdom. Traps baited with the synthetic pheromone blend captured males of P. californicus (southwestern Idaho, southern California, and northwestern Utah), P. lecontei (southern California and northwestern Utah), and six additional species of Prionus: Prionus integer LeConte (southwestern Idaho), Prionus imbricornis (L.) (Georgia), Prionus laticollis (Drury) (Georgia), Prionus linsleyi Hovore (north central Arizona), Prionus aztecus Casey (northern Mexico), and Prionus coriarius (L.) (East Anglia, United Kingdom). These findings demonstrate that synthetic 3,5-dimethyldodecanoic acid can be used to assess the geographic distribution and local abundance of many Prionus species and therefore may be of value for monitoring threatened and endangered species of this genus, and for managing those that are pests.

Understory cover crops in pecan orchards: Possible management systems

Annual legumes and mixtures of annual legumes and grasses can perform several functions as understory cover crops in pecan orchards, such as providing nitrogenrich organic matter to improve soil fertility, or by sustaining lady beetles and other arthropods that may aid the biological control of pecan pests. Remaining questions concern selection of appropriate plant materials; whether to use cover crops singly or in mixtures; how to ensure reseeding as well as a substantial N contribution; whether, when, and how to use mowing and tillage; and fertilization options. Different considerations apply when dealing with cool- vs. warm-season cover crops. With minor adjustments, growers could adapt present cultural practices to include cool-season cover crops. These could be used throughout the orchard, by establishing appropriate self-reseeding species and avoiding both excessive mowing and indiscriminate placement of N-rich fertilizers. Within alleys, alternating 2-m strips of cool-season cover crops could be tilled in mid to late April or allowed to mature. The tilled strips would supply N to pecan trees immediately, whereas the adjoining untilled (remnant) strips could be mowed after seed is mature, to ensure dispersal of seed and reestablishment of cover crops over the entire alley. Cool-season annual legumes that die or are killed in late spring will probably furnish N and other nutrients at a suitable time, particularly in orchards with sprinkler irrigation. Warm-season cover crops, if desired, should be restricted to alleys to reduce possible competition with pecan. Alleys provide better illumination than do tree rows during periods when pecan trees are in leaf, and the tillage mentioned above will encourage emergence of warm-season cover crops. If these die or are killed in late summer or early fall, timing of N release may not be optimal, in the absence of adequate irrigation. Many options and tradeoffs need to be explored before choosing a cover-crop system. Attimes, several objectives may appear to conflict, and even delicately-managed mixtures of species may not fulfill all the desired functions.

Interactions in entomology: aphids, aphidophaga and ants in pecan orchards.

Three methods for conserving aphidophaga were tested in multiple factor controlled field experiments over two seasons in four pecan, (Carya illinoensis Wangenheim (K. Koch)) orchards. Two of the orchards were planted in the 1920s and had closed canopies; and the other two were planted in 1976 and 1985 and had open canopies. Intercrops of hairy indigo (Indigofera hirsuta L.) and hemp sesbania (Sesbania exaltata [Rafinesque-Schmaltz] Cory), sown as summer annuals in strips between tree rows, a chemical barrier sprayed on the tree trunk preventing foraging of the red imported fire ant (Solenopsis invicta Buren) in the tree crown, and a predator attractant were tested in these experiments. Significant interaction effects were found in blackmargined aphid (Monellia caryella (Fitch)), ladybeetle (Coccinellidae), and red imported fire ant abundance. On most sample dates there were no differences among treatments in abundance of pecan aphids or aphidophaga, whereas, on certain sample dates aphids were significan...

Tarnished plant bug (Hemiptera: Miridae) on selected cool-season leguminous cover crops.

Replicated field trials indicated that tarnished plant bug (TPB), Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae) attained relatively-high densities on hybrid vetches, Vicia sativa L. X V. cordata Wulf cv ‘Cahaba White’ and ‘Vantage’, lower densities on crimson clover, Trifolium incarnatum L. cv ‘Dixie,’ and particularly-low densities on subterranean clover, Trifolium subterraneum L. cv ‘Mt. Barker’. Densities of TPB were also relatively low on an additional 10 types of subterranean clover, including 7 cultivars representing T. subterraneum, 1 cultivar of T. brachycalycinum Katznelson and Morley, and 3 of T. yanninicum Katznelson and Morley. Field longevity trials indicated that late-instar and adult TPB lived longer when caged on crimson clover than on hybrid vetch, which in turn supported better survival than did subterranean clover. When adult TPB were caged on hybrid vetch or subterranean clover with or without floral and fruiting structures, there was no evidence that the presence of thes...

Imidacloprid Insecticide Slows Development of Pierce's Disease in Bunch Grapes

Six cultivars of bunch grapevines Vitis labrusca (L.) and V. vinifera (L), ‘Cabernet Franc’, ‘Canadice’, ‘Flame Seedless’, ‘Johannesburg Riesling’, ‘Mars’ and ‘Reliance’ when treated at planting an...

Sesbania exaltata (Rafinesque-Schmaltz) Cory (Fabaceae) as a Warm-Season Cover Crop in Pecan Orchards: Effects on Aphidophagous Coccinellidae and Pecan Aphids

ABSTRACT The effects of warm-season cover crops on aphidophagous Coccinellidae and pecan aphids were evaluated in replicated studies at three commercial pecan orchards in southern Georgia. Each orchard featured cover-cropped plots dominated by sesbania (Sesbania exaltata [Rafinesque-Schmaltz] Cory) and control plots containing resident vegetation. Sesbania was the only understorey plant that harboured substantial densities of alternative prey, such as cowpea aphid (Aphis craccivora Koch) and bandedwinged whitefly (Trialeurodes abutilonea [Haldeman]), suitable for Coccinellidae. When densities of pecan aphids dropped during July or August, whitefly-infested understorey stands of sesbania arrested and retained high densities of convergent lady beetle (Hippodamia convergens Guerin-Meneville) and the principally-arboreal Olla v-nigrum (Mulsant). In two separate studies, highly significant differences were found for season-long mean densities of pooled adult lady beetles: densities were 125 and 48 times greate...

Conservation of aphidophaga in pecan orchards

Publisher Summary Foliage-feeding aphid species infest pecan orchards and damage them by causing early defoliation leading to reductions in staminate and pistillate flowers and nut production. Long-term orchard management practices are effective in pecan orchards to stabilize the abundance of imported and indigenous natural enemies. The producer has a long-term investment in the orchard and can implement conservation techniques over several years. Conservation techniques of intercropping with sesbania alone, the combination of mowed sod and ant exclusion, and the combination of intercropping with hairy indigo and ant exclusion has reduced pecan aphid populations in Georgia. The development and implementation of an alternative to chemical control of pecan aphids require greater monitoring and another level of decision making for producers. Producers of improved cultivars typically apply one spray for pecan nut casebearer, one spray for early season hickory shuckworm, and three sprays for the late season pest complex (that is, pecan weevil, kernel-feeding hemipterans, leafminers, aphids, mites, and late season hickory shuckworm). Chemical control of foliage-feeding insects is achieved by mixing a specific larvicide, aphidicide, or miticide with the principal insecticide for nut pests.