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Cucumber Beetles and Bacterial Wilt of Cucurbits

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Cucumber Beetles and Bacterial Wilt of Cucurbits ALABAMA A&M AND AUBURN UNIVERSITIES M ANAGEMENT O F Cucumber Beetles And ANR-1026 Bacterial Wilt Of Cucurbits Beetle Identification soil and the next generation of ons and cucumbers, they spread beetles emerge. the bacteria through their feces Striped and spotted cucum- and contaminated mouthparts. ber beetles can be serious pests Multiple generations of cu- of cucurbit crops (cucumber, cumber beetles occur in Studies in Alabama have melon, pumpkin, squash) grown Alabama each season, with more shown that the severity of wilt in Alabama. Both beetles are generations produced in the disease on cucumber in the field south half of the state than in is proportional to the number of about 1⁄4 inch long, 1⁄8 inch wide, and yellow-green. The the north. Cucumber beetle beetles feeding on the plant. striped cucumber beetle adult adults emerge very early in the Even low beetle numbers (one has three black stripes along the spring and may feed on weeds per plant) are sufficient to cause length of the body, and the spot- before moving into nearby plant- infection. ted cucumber beetle has 12 ings of cucurbits. Young plants are more sus- black spots on its back (Figure ceptible to infection than older 1). Spotted cucumber beetles at- Beetle Feeding plants. In addition, young plants tack other crops in addition to Damage and Spread are more attractive to beetles cucurbits (such as corn, sweet- and are likely to be fed upon potato, peanuts), but striped cu- Of Bacterial Wilt more heavily than older plants. cumber beetles prefer cucurbits Disease On young plants, the first to other crops. signs of beetle-feeding damage Feeding by large numbers of are observed on cotyledons and cucumber beetles can kill or stems (Figure 2). Beetles feeding stunt early-season cucumber and on infected plants can spread squash seedlings or young trans- the bacteria to healthy plants. In plants. Beetles may also feed on addition, beetles seem to be at- watermelon and muskmelon tracted to wilted leaves, thus in- rind later in the season causing creasing their exposure to the cosmetic damage that reduces pathogen and its spread. the value of the crop. In addition to feeding dam- age, cucumber beetles are the only known vectors of bacterial Figure 1. The adult spotted cucum- wilt disease caused by the ber beetle has 12 black spots on its back. pathogen Erwinia tracheiphila. Bacterial wilt is a serious disease Adult females deposit eggs of cucumber and muskmelon in the soil at the base of the and to a lesser extent, squash plants. The eggs hatchARCHIVE and the and pumpkin. The bacteria do larvae, or immature stage, feed not survive in crop debris, soil, on the underground plant stem or on seeds. It is thought that and root tissue. The larvae can the pathogen overwinters in cause some damage by under- weeds that show no disease ground feeding, but the primary symptoms, and that beetles pick economic damage to cucurbits up the pathogen when feeding results from the adult beetles on the weeds in early spring. In feeding on foliage, stems, and Figure 2. Cucumber beetle feeding the spring when beetles become damage on cotyledons and stem of flowers. The larvae pupate in the active and begin feeding on mel- cucumber. Visit our Web site at: www.aces.edu Once the bacteria enter the Management ticularly if the field has a history plant, they multiply and move of bacterial wilt disease. quickly through the vascular sys- Insecticides And Scouting If many beetles are observed tem. In the process, they inter- The first 2 to 3 weeks after feeding on weeds or plants fere with the movement of water plant emergence is the critical along the field edges, make a fo- and nutrients and this results in period for cucumber beetle con- liar insecticide application within the drooping, wilting, and death trol. At this time, plants are most 24 to 36 hours in anticipation of of the aboveground parts of the attractive to beetles and most the migration of beetles into the plants. Plants usually show susceptible to disease infection. field. Because beetles are highly symptoms between 5 to 14 days If heavy cucumber beetle popu- mobile and plants produce new after infection. The first sign of lations are expected, it may be growth rapidly, twice-weekly ap- wilt is a distinct flagging of indi- advisable to apply the systemic plications of foliar insecticides vidual leaves, followed by wilt- soil insecticide carbofuran may be required. Pyrethroid in- ing of adjacent leaves, and the (Furadan 4F) at planting. This in- secticides generally have long entire vine (Figure 3). The wilt- secticide has a special registra- residual activity but are highly ing quickly spreads as the vascu- tion for use in Alabama on cu- toxic to some beneficial insects. lar system becomes blocked by cumber, melons, squash, and Their use may result in out- bacteria and the entire plant pumpkins for cucumber beetle breaks of secondary pests like eventually wilts and dies. Once control. Carbofuran must be ap- aphids. Because watermelon is the plant is infected it cannot be plied directly into the seed fur- not susceptible to wilt disease, saved. The only way to prevent row; it cannot be used as a foliar protection with insecticides is the spread of bacterial wilt is to spray. It may also be mixed with only necessary when plants are control beetle feeding on the liquid fertilizer. Please refer to small and high beetle popula- plant. the Furadan 4F label for rates, tions are feeding on the plants application guidelines, and re- or fruit. Please refer to the table strictions. Some research has below for a listing of recom- shown that carbofuran may pro- mended foliar insecticides for vide 4 to 6 weeks of beetle con- cucurbit crops. trol, while other tests have Foliar insecticide applications shown only 1 to 2 weeks of con- will probably not be necessary trol. or cost-effective after beetle pop- In any event, high beetle ulations begin to decrease and populations may still transmit the plants mature (usually in 2 to the wilt pathogen before the in- 4 weeks after plant emergence). Figure 3. Symptoms of bacterial wilt secticide inside the plant can Older plants are much more tol- disease. have an effect. Therefore, even if erant of beetle feeding damage carbofuran is used, it is advis- and bacterial wilt infection than able to monitor plants for pres- young plants. Frequent use of A Diagnostic Field ence of beetles, and to apply a some foliar insecticides may also foliar insecticide if the beetles reduce fruit set because the Test For Bacterial seem to be surviving the carbo- chemicals may cause abortion of Wilt Disease furan treatment. A secondary ad- flowers. In addition, foliar insec- ticides kill beneficial insects like A good test for diagnosing vantage of carbofuran is that it predators, parasites, and polli- wilt disease in the field is to cut may provide some control of soil nating bees. the stem at the base of the plant insects like seed maggots and and hold the two cut ends to- cutworms. A new type of insecticide, gether for about 10 seconds. As Whether or not carbofuran is Adios, is now registered for use the ends are slowly movedARCHIVEused, it is important to begin on cucumbers, squash, melons, apart, a white, sticky “bacterial scouting fields immediately after and pumpkins. Although used as ooze” will appear as a string be- plant emergence or transplanting a foliar spray, Adios acts as a tween the cut ends. This “ooze” to detect beetles on plants. A bait because it contains a cu- is the bacteria that have multi- recommended foliar insecticide cumber beetle feeding stimulant plied in the water-conducting should be applied if beetles are along with 13% carbaryl insecti- cells. Also, the cut-ends ooze a detected on plants during the cide. When Adios is sprayed on whitish substance when placed first 2 to 3 weeks after plant foliage, beetles are stimulated to in water. emergence or transplanting, par- feed on the compound and are 2 Alabama Cooperative Extension System Recommended Insecticides for Cucumber Beetle Control on Cucurbits Insecticide Amount of Minimum days Comments formulation from last application per acre to harvest carbofuran FURADAN 4F 3.8 fl. oz. per Apply in the furrow at planting. Furadan 4F may be 1,000 feet of row not applicable mixed with water or liquid fertilizer. Furadan is a restricted use insecticide. carbaryl SEVIN 80WP 1.25 lb 0 ADIOS 0.5 - 0.75 lb 0 Adios acts as a bait that contains a beetle feeding stimulant and carbaryl insecticide. endosulfan PHASER 0.66 - 1.33 qt 2 Phaser and Thiodan are not registered for use on THIODAN 3EC 0.66 - 1.33 qt 2 pumpkin. esfenvalerate ASANA XL 5.8 - 9.6 fl oz 3 Asana is a restricted use insecticide. permethrin AMBUSH 2EC 6.4 - 12.8 fl oz 0 POUNCE 3.2EC 4 - 8 fl oz 0 Ambush and Pounce are restricted use insecticides. killed by the carbaryl. In field Row Covers tests, Adios has provided cucum- For organic growers who ber beetle control ranging from prefer not to use insecticides, lower to or equal to that of foliar cheesecloth or other suitable insecticides. It has no harmful row cover material may be used effect on beneficial insects, in- to protect plants from beetles cluding pollinators (because in- during the period from emer- sects other than cucumber bee- gence to bloom. Row covers tles are not stimulated to feed on must be removed before flowers the compound). appear to allow pollination by insects.
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