Sweet potatoes are subject to attack by soil and foliage insect species throughout the growing season. Sweet potato weevils may be a problem in storage. Insect damage causes economic losses in quality and overall yield, and growers sustain significant losses to root-feeding soil insects.
Root-feeding Insects:
Banded cucumber beetles, whitefringed beetles and some kinds of flea beetles – The larvae chew shallow holes in the growing root, which affects the grade of the harvested root. Foliar-applied insecticides are applied to control the adult stages of these pests to prevent them from laying eggs in the soil. Insecticide applications should be made only when the pests are present in sufficient numbers to warrant control (see IPM section).
Control – Spray foliage with 0.5 pounds technical Carbaryl or Thiodan per acre. Imidan 70-W may be sprayed on the foliage at 1 1/3 pounds per acre. This product must be applied in water adjusted to pH near 5.0 to 5.5. A maximum of five applications of Imidan may be made during the growing season. Begin applications about three weeks after plant set if the banded cucumber beetle is present. Continue applications weekly until one week before harvest. Shorten spray intervals if necessary to keep the numbers of banded cucumber beetles to at low level. Penncap-M may be sprayed on foliage for whitefringed beetles at 2-3 pints per acre. Do not exceed 24 pints per season, and do not apply to seedbeds. Capture 2 EC may be used to control the banded cucumber beetle, whitefringed beetle and some kinds of flea beetles. Application to foliage should be made at 0.05 pounds active per acre (3.2 oz. formulated chemical). Put chemical in 10 gallons water per acre or more for best results. Do not apply within 30 days of harvest. Follow label restrictions. Baythroid XL may be sprayed for cucumber beetles at a rate of 1.6 - 2.8 ounces per acre not to exceed 16.8 fluid ounces in a season. A recently registered insecticide, Assail 30SG, is an effective chemical for cucumber beetles, flea beetles, aphids and leafhoppers. Use Assail at 1.5 - 4.0 ounces per acre. SG is "soluble granules" and must be weighed.
Wireworms, Grubs and Rootworms – These are larvae of click beetles, June bugs and banded cucumber beetles, respectively, that tunnel or chew large holes in the developing sweet potato roots. Preplant, soil-incorporated insecticides are applied to control the immature stages of these pests present in the soil at the time of application. These chemicals provide a residual control for 4 to 6 weeks.
Suppression – Mocap or Lorsban: apply 30 pounds of 10% Mocap granules per acre (or 0.5 gallons of 6 pounds/1 gallon EC) or 13.3 pounds of 15% Lorsban granules per acre (or 0.5 gallons of Lorsban 4E) as a preplant application. For Mocap, open rows to a 15-18 in furrow, apply Mocap to cover furrow, then row up using a “hipping ridger.” Apply Lorsban on a broadcast basis, disk and row up. Capture may be used as an in-furrow application as a planting time treatment. Apply Capture at a rate of 0.3 pounds active per acre as an in-furrow spray or T-band at planting.
Foliage-feeding Insects:
Aphids, Flea Beetles and Whiteflies – Apply Admire 2F to the soil and incorporate to control aphids and whiteflies (vectors of virus diseases). Rates per application range from 13-19 fluid ounces per acre. Using a row spacing of 42 inches translates to 16 fluid ounces per acre or 0.25 pounds active ingredient per acre.
Use Platinum 2F (thiamethoxam) applied in-furrow at planting or as a lay-by-shanked application to control aphids, whiteflies and flea beetles. Recommended rates per application range from 5-8 fluid ounces/acre. Do not apply Platinum as a broadcast foliar spray with ground or aerial equipment. Follow mixing directions and read the label carefully.
Foliage-feeding loopers, Beet armyworms and other Lepidoptera species – When defoliation reaches 35% or higher, apply Spin Tor 2SC for control of loopers and armyworms. Recommended rates range from 4-6 ounces formulated product per acre. This rate equals 0.062 – 0.094 pounds active ingredient per acre. A new insecticide recommended for control of lepidopterous larvae is Rimon 0.83 EC at 9.0 fluid ounces per acre. Rimon is a third generation Chitin inhibitor and an excellent IPM material because of its safety to beneficial insects. Intrepid 2F received a 24C label this year. It effectively controls both loopers and beet armyworms. Apply at the rate of 6 - 10 fluid ounces per acre. Baythroid XL at a rate of 1.6 - 2.8 fluid ounces per acre may also be used to control loopers. Read all labels carefully and follow labeling instructions.
CULTURAL & CHEMICAL MEASURES
TO CONTROL SWEET POTATO WEEVILS
Sweet potato weevil larvae attack the roots of the sweet potato plant, tunneling through the roots as they feed. Sweet potatoes are susceptible to attack by the sweet potato weevil at any time during the growing period as well as in storage.
All cultural and sanitation practices for control of the sweet potato weevil should be followed. This includes acquiring weevil-free seed, cutting vines or slips (rather than pulling), destroying all potatoes left in fields, controlling weevils in the seedbed and destruction of the seedbed when plant production is finished. Also, if infestation is bad, spray fields with 0.5 pounds Thiodan and 1.0 pounds Carbaryl per acre. Pheromone traps should be placed in fields to help determine weevil population levels. If several weevils are caught per trap per night, then foliar spray applications should be made.
In the Field – Rotate field plantings. Plant the new crop as far away as possible from the plantings of the previous year. Apply weekly applications of Penncap-M at 2-3 pints/acre, 0.5 pounds Thiodan, 1 1/3 pounds Imidan 70 WSB or 1.0 pounds Carbaryl to suppress sweet potato weevil populations in the field.
In the field, apply Capture at a rate of 0.05 pounds (3.2 ounces formulated chemical) to foliage in 10 gallons of water or more per acre. Do not make more than two applications with Capture 2 EC. Do not apply within 30 days of harvest. Observe label restrictions. Baythroid XL may be sprayed for sweet potato weevil adults at a rate of 1.6 - 2.8 ounces per acre not to exceed 16.8 fluid ounces in a season.
At Harvest – Seed sweet potatoes should be selected at harvest from fields apparently free of sweet potato weevil. Destroy all vines and roots left in the field. If seed potatoes appear to be heavily infested, consider purchasing weevil-free seed from a weevil-free area.
In-Storage – Remove all old sweet potatoes from the storage area at least one month before storing the new crop. Store only those potatoes that are apparently weevil-free and reasonably clean. Treat potatoes going into storage with 5% Imidan dust (2-4 ounces per bushel) using an applicator approved by the Louisiana Department of Agriculture and Forestry.
In Seedbeds – Locate seedbeds away from sweet potato storage and last season’s plantings.
Weevils may enter seedbeds from outside sources. To minimize the infestation from invading weevils, apply Thiodan (0.5 pounds technical per acre) or Carbaryl (1.0 pounds per acre) to plants weekly beginning when plants first emerge (or when the plastic cover is stripped from the seedbed) and continuing as long as the seedbed is used. Almost all weevil eggs in plant stems are found near the soil surface, so plants should be cut at least an inch above the soil level. Destroy the seedbed when it is no longer needed.
WARNING: Re-entry time for workers entering groves and/or treated fields should be strictly observed. Be sure to check for this information.