Charles G. Summers

Integrated Pest management in Forage Alfalfa

Alfalfa, Medicago sativa L., is among the most prized of forages, and is grown worldwide as a feed for all classes of livestock. It is one of mans oldest crops, and its cultivation probably predates recorded history. In addition to its versatility as a feed, alfalfa is well known for its ability to improve soil structure and, as a legume, is an effective source of biological nitrogen. As a perennial crop, alfalfa has a lifespan approaching 5 years, but in some areas of the world fields may remain productive for considerably longer. Such a long stand life affords ample time for the establishment and development of a diverse community structure by an abundance of organisms. In spite of system perturbations caused by frequent harvests and occasional pesticide applications, an alfalfa field provides a temporal stability which is uncommon among field crops. As a result of this stability, alfalfa supports an immense diversity of flora and fauna which, at times, exceeds that of riparian ecosystems. While most of alfalfas inhabitants have little or no impact on it as a crop, a few are capable of causing extensive damage. Arthropods, plant pathogens, weeds, vertebrates, and plant parasitic nematodes can all cause significant yield and/or quality reductions and frequently contribute to shortening the productive life of the stand. This paper reviews the major strategies which have been developed to manage many of these alfalfa pests including: host plant resistance; cultural controls, such as harvest strategies, irrigation management, sanitation, planting schedules, and crop rotation; mechanical and physical controls; chemical control; and biological controls. Multiple pest interactions, e.g. insect-insect; insect-disease; insect-weed, and their management are discussed. Potential conflicts arising from the use of strategies which may reduce one pest but exacerbate others are also examined. A cross index of management strategies and their role in managing multiple pests is provided. Computer models, both ecological and economic, and their role in alfalfa pest management are discussed. Selected information sources on alfalfa and alfalfa IPM available over the Internet are listed. Alfalfas role in the agricultural landscape, as it relates to pests, natural enemies, and pest management in other cropping systems as well as its role in crop rotation, is considered.

Reflective mulches for management of aphids and aphid-borne virus diseases in late-season cantaloupe (Cucumis melo L. var. cantalupensis)

Abstract A complex of aphids and several mosaic virus diseases can cause major losses in cucurbitaceous crops grown in the inland valleys of California. Three field experiments were conducted to test and compare the effectiveness of reflective polyethylene and biodegradable, synthetic latex spray mulches for management of aphids and aphid-borne virus diseases of late-season cantaloupe ( Cucumis melo L. var. cantalupensis cv. Primo) in the San Joaquin Valley. Beneficial responses were obtained from the reflective mulches, under conditions of high aphid populations and virus inoculum potential, during each of the experiments. Aphid numbers on leaves of plants growing over mulches were consistently lower than on those growing over bare soil. Onset of symptoms of cucumber mosaic cucumovirus, and watermelon mosaic and zucchini yellow mosaic potyviruses, were delayed 3–6 weeks in plants growing over the mulches, which was critical for initiation of normal flowering and fruiting. High virus disease incidence (100% incidence of foliar symptoms) reduced cumulative, marketable melon yields (number of fruit, fresh weight, and size) in the control plots to near zero in two of the three experiments. In each of the experiments, polyethylene or spray mulch treatments which completely covered each planting bed provided at least 9.5- and 2.5-fold increases in marketable yield, respectively. In the first two experiments, reflective mulches would have provided the difference between salable crops and total crop loss. Partial bed coverage with spray mulch, and alternate row applications of polyethylene film mulches, were less effective than complete coverage of every planted row.

Use of UV reflective mulch to delay the colonization and reduce the severity of Bemisia argentifolii (Homoptera: Aleyrodidae) infestations in cucurbits

Abstract Effectiveness of UV reflective plastic mulch for the management of silverleaf whitefly ( Bemisia argentifolii Bellows and Perring) was evaluated in selected cucurbits. The reflective mulch repelled silverleaf whitefly adults in pumpkin ( Cucurbita maxima Duchesne), cucumber ( Cucumis sativus L.) and zucchini squash ( Cucurbita pepo L.). Reduced colonization by B. argentifolii adults resulted in reduced populations of nymphs and a delay and reduction in the incidence of silverleaf in pumpkin and zucchini squash. Reflective mulch was as effective in reducing nymphal B. argentifolii populations as was a pre-plant soil application of imidacloprid. Zucchini squash, pumpkin and cucumber yields were significantly higher in plants grown over reflective mulch than in those grown over unmulched soil. Zucchini squash yields from plants grown over reflective mulch also were higher than from plants grown in plots receiving a pre-plant application of imidacloprid. This study confirmed that UV reflective plastic mulch can be used to manage B. argentifolii and the mulches give protection equal to that provided by imidacloprid.

Overwintering of Corn Leafhopper, Dalbulus maidis (Homoptera: Cicadellidae), and Spiroplasma kunkelii (Mycoplasmatales: Spiroplasmataceae) in California’s San Joaquin Valley

Abstract A 3-yr study was conducted in California’s southern San Joaquin Valley to determine the overwintering survival of the corn leafhopper, Dalbulus maidis (DeLong and Wolcott), and the mollicute, Spiroplasma kunkelii, the causal agent of corn stunt disease. Corn leafhopper populations were sampled from November to March using yellow sticky cards, D-vac suction samples, and inspection of volunteer corn plants and spring planted corn. S. kunkelii presence was determined by sampling sentinel plants placed in the field during the winter, leafhoppers collected throughout the winter, and evaluation of volunteer plants over the winter and spring planted corn. Leafhoppers were collected on yellow sticky cards throughout the winter during all 3 yr. They were also regularly recovered from alfalfa, Medicago sativa L., winter forage (wheat, Triticum aestivum L., and triticale, Triticale hexaploide Lart. and riparian areas by D-vac suction sampling. Females constituted the majority of leafhoppers (>80%) recovered on both sticky cards and from D-vac samples. S. kunkelii was recovered from leafhoppers throughout the winter, from sentinel plants, and in spring planted corn. Volunteer plants were determined to be a critical key in leafhopper overwintering, and consequently, the survival of S. kunkelii. Volunteers extended the season by as much as 2 mo, thus shortening the period of time the leafhoppers were forced to go without a food source. The possible reasons for a shift in the leafhopper from cyclic pest to persistent pest in the region are also discussed.

Management of Corn Leafhopper (Homoptera: Cicadellidae) and Corn Stunt Disease in Sweet Corn Using Reflective Mulch

Abstract Plastic reflective mulches significantly reduced populations of corn leafhopper, Dalbulus maidis (DeLong & Wolcott), adults and the incidence of corn stunt disease caused by Spiroplasma kunkelii (CSS) in late planted sweet corn (Zea mays L.). The reflective mulches were more effective than were either foliar or soil applied insecticides in managing both the leafhopper and the pathogen it transmits. Yields of marketable ears were 1.5 to 2 times greater in reflective mulch plots than from fallow plots. This was due to larger ears (individual ear weight and length) rather than an increase in the number of ears. The use of reflective mulches provides an alternative strategy to insecticides in the management of both D. maidis and corn stunt disease. Such a strategy may prove useful to growers in Latin America and to limited resource growers and organic growers in the United States who wish to grow corn without the use of insecticides.

Strip Cutting Alfalfa for Lygus Management: Forage Quality Implications

Strip cutting is used to limit lygus migration from alfalfa into susceptible neighboring crops. Hay growers are concerned that the uncut strips negatively impact quality and marketability of alfalfa from subsequent cuttings. The objective of this trial was to determine if blending the hay from the uncut strips with the new growth could mitigate reductions in quality and improve marketability. There were negative impacts of mixing old hay with the new growth alfalfa in both 2000 and 2001. As old growth was added in 25% increments to the new forage in the bale, crude protein values declined by 1 to 2% and ADF values increased by 1 to 3.5%. Since ADF is used to calculate TDN, increases in ADF will have a significant impact on the value of the forage. There was no significant reduction in crude protein value when 7 or 14% old growth alfalfa was present in bales as compared to bales containing 100% new growth. With respect to ADF, the only significant difference was between the new hay and the hay containing 14% old growth. When visually evaluating hay, there appear to be subtle changes in appearance when old growth is blended with new growth that can be detected. The most sensitive characteristics are color and overall quality. Growers need to assess the requirements of their market, and determine the best strategy for managing the alfalfa strips left in fields for the purpose of lygus management based upon the expected reductions in quality reported here.

Economic Analysis of Three Soil-Surface Practices for Production of Fresh Market Tomato (Solanum lycopersicum L.)

Plastic and cover crop mulches are widely used in a number of vegetable crop production areas, but they currently are not commonly used in California. Evaluations of the effects of silver UV reflective plastic (RP) and cool-season cover crop (CC) mulches relative to the standard, bare-ground production system (ST) on growth, yield, and costs and returns of tomatoes were conducted in California. Biomass increased earlier over the RP mulch and was nearly twice that of both the ST and CC mulch at harvest. Yields were higher for RP (62,022 kg ha−1) and lower in the ST (37,467 kg ha−1) and CC mulch (25,005 kg ha−1) systems in 1999, and also highest in the RP in 2000. Costs in both the RP and CC mulch systems were higher than in ST system in both years and, based on returns on investment, were warranted in the RP system in both years, but only in 1999 in the CC system compared to the ST system. RP mulches may thus be a viable alternative for fresh market tomato production in California. CC mulches may be a useful alternative if productivity can be maintained using sustained no-tillage techniques.