Potatoes and tuberous and corm vegetables (Irish and sweetpotato)
Potato: Colorado potato beetle, Leptinotarsa decemlineata (Say), Coleoptera: Chrysomelidae
|
Photo 131 |
|
Photo 132 |
|
Photo 133 |
Biology: Adult Colorado potato beetles are about 13 mm long and light yellow and black in color (Photo 131). Each forewing has 4 longitudinal black lines. In the spring adults emerge from the soil, mate and deposit up to a few hundred eggs on foliage of host plants. Eggplant and potato are preferred hosts although tomato, pepper and solaneous weeds, esp. horsenettle, are also attacked. Several eggs are generally deposited on the foliage of a single plant (Photo 132). Larvae (Photo 131) hatch in approximately one week and feed on foliage (Photo 133). Consumption of large amounts of foliage quickly occurs and potato plants can be stunted. Larvae are wingless and reddish-brown in color. After feeding for about 3 weeks, larvae move to the soil, pupate and begin the cycle again. In Arkansas two generations occur each year.
Management: The most susceptible stage of potato to the Colorado potato beetle is just after emerging when plants are small and not vigorously growing. Planting when temperatures are warm and use of irrigation and fertilization will promote rapid plant growth and resulting damage from beetles will be minimized. If beetle numbers increase beyond acceptable levels, use of insecticides may be warranted. Several traditional contact insecticides are effective in Colorado potato beetle management in Arkansas. Beneficial insects are also important in regulation of Colorado potato beetles. Minimizing the availability of host plants by plowing under eggplants after harvest and removal of solaneous weeds will aid in management. Recent increases in occurrence of Colorado potato beetle in Arkansas may be related to the use of reduced tillage practices in soybean. Producers are now permitting weeds to grow longer in the spring and early summer in soybean fields. Solenacious weeds are common and may provide an expanded host plant period for the Colorado potato beetle population to increase.
Back to Top
Potato: Cutworm, Agrotis spp., Lepidoptera: Noctuidae
Biology: Adult cutworms are dark gray moths with wingspans approaching 5 cm. After mating, females lay eggs on the host plant and larvae emerge in three to six days (Photo 134). As larvae develop the stem of seedling plants is often cut just above the soil line. Cutworms attack most vegetable plants.
Management: Adult cutworms are attracted to fields with plants or weeds where they deposit their eggs. Thus maintaining the field free of plants for at least two weeks prior to planting, will reduce the cutworm problem. Crop rotation, esp. beans, can reduce future cutworm problems. Soil insecticides may be used with some success and will likely remain a critical element of cutworm management. In fields with persistent cutworm problems, incorporating insecticides into the soil has proven effective. Application of insecticides to foliage may be attempted in fields with problem cutworm populations but may not provide acceptable results.
Back to Top
Potato (sweet): Sweet potato weevil, Cylas formicarius (Fabricius). Coleoptera: Curculionidae
Description: Sweet potato is grown commercially only in the southeastern corner of Arkansas. In this area, the sweetpotato weevil is a relatively common pest. Elsewhere in the state, the weevil only sporadically occurs in small gardens. Adult weevils are elongated and are about 7 mm in length (Photo 135). The head is black, thorax reddish to orange and the upper abdomen is a metallic blue. Adults likely overwinter in Arkansas but may also migrate into the state on infested transplants or tubers. Once sweet potato begins to grow, adult weevils chew shallow holes in the stem near the soil line and deposit eggs. Larvae hatch in one week or less and feed internally within lower stems and the tuber. At maturity, larvae are legless, whitish grubs about 9 mm in length. Damage is in the form of small diameter tunneling in both the tuber and within the vine. Sweetpotato weevil feeding also imparts an off taste in the sweet potato rendering the potato unfit for consumption. Several generations occur annually in Arkansas.
Management: In Arkansas, obtaining sweet potato transplants free of sweetpotato weevil reduces movement into the state from areas with high weevil populations. If possible, fields should be located away from areas of previous sweet potato production. Sandy soils limit the exposure of the tuber to adult weevils. Sanitation, i.e., destruction of plants and non-harvested tubers after harvest, reduces the availability of the host. Storage of sweet potatoes should be away from the field and by use of controlled atmosphere, weevil populations on stored potato can be reduced. Use of soil insecticides applied at planting may provide some control. Also, some foliar applied insecticides, particularly systemics, may prove successful.
Back to Top
Potato: White grub, Phyllophaga spp. , Coleoptera: Scarabaeidae
|
Photo 136 |
|
Photo 137 |
|
Photo 138 |
Biology: White grub adults (Photo 136) are attracted to fields with vegetation, esp. grasses including corn. Here they deposit eggs into the soil and larvae later hatch and feed on plant roots and tubers (Photo 137). Larvae have a whitish abdomen and tan head and legs (Photo 138). When prodded the larvae curl into a “C” shape characteristic of the Scarabaeidae family. At maturity, larvae are about 25 mm in length. Larvae may require up to three years to complete development.
Management: Several steps at white grub management are suggested and should help to reduce, but not eliminate, the impact of the insect on vegetable production. But, first a note of caution should be mentioned. Insects in the soil are often very difficult to manage and low numbers of white grubs are likely best managed by tolerating them. If numbers are deemed high the following are suggested. Maintain the field free of weeds, esp. grasses, for as much time as possible prior to planting. This practice may reduce the field attractiveness to white grub adults. Deep plowing should have some effect on exposing the larvae to birds and beneficial organisms. Crop rotation with less attractive host plants, esp. legumes or beans, should be practiced. In areas with persistent white grub populations, soil insecticides will likely remain a useful tool for white grub management. Incorporating insecticide into the soil is effective. Milky spore disease may provide some white grub suppression.
Back to Top
Potato: Wireworm, Coleoptera: Elateridae
Biology: Several species of wireworms occur in Arkansas and descriptions of the different species vary. In general, wireworm adults, also known as click beetles, are dark brown hard bodied beetles. The term “click” comes from the ability to snap the hinge between the thorax and abdomen resulting in a flip that rights the upturned insect. Size varies but adult wireworms in potato are about 20 mm long. Larvae occur in the soil. Although the larvae of some species are white, the most common in Arkansas is tan and at maturity about 20 mm in length (Photo 139). True legs are evident and the head is somewhat flattened. Wireworms occur throughout the state. The biology of wireworms is also quite variable. Some species complete two generations per year while some require up to 5 years for a single generation. In general adults emerge from overwintering larvae in the spring and search for grassy fields. Eggs are laid in the soil usually where grasses are available for the larvae to feed. When potato is planted the tubers are burrowed into and larvae tunnel throughout the potato (Photo 140).
Management: In Arkansas, avoidance of recently plowed grassy fields including pastures will reduce the likelihood of damage from wireworms. Crop rotations may reduce damage but with wireworms that require multiple years for development, damage may be substantial. Although the use of soil insecticides applied at planting may provide some control, wireworm problems may persist. Foliar insecticide application to seedlings is of no benefit.
Back to Top
|
