Southeastern U.S. Vegetable Crop Handbook - 2023 - 109

production season, but damage from these insects increases late
season. Feeding injury results in unsightly blemishes on the roots
at harvest. The larval stage lasts from 8-30 days depending on the
temperature and food supply. Pupae are found just below the soil
surface. Adults will emerge in approximately one week. Numerous
generations of these insects can develop and injure sweet potatoes
throughout the production season. Soil applied insecticides
can reduce damage from these insects if applied close to planting.
Adults should be scouted weekly during the production season
and labeled insecticides should be applied when the number of
beetles sampled reaches or exceeds the treatment threshold of 2
beetles/100 sweeps.
Tortoise Beetle: Generally, damage by tortoise beetles threatens
newly set plants or plants under stress. Leaves of infested plants
are riddled with large, round holes. Adults and larvae which feed
on sweetpotato foliage include: mottled tortoise beetle, striped
tortoise beetle, and argus tortoise beetle, blacklegged tortoise,
and golden tortoise beetle. Isolate plant beds and control morningglory.
Monitor movement of ornamental sweetpotatoes which
often contain tortoise beetles and other insects. Apply insecticides
to young plants if needed. Control beetles in plant beds and
fields.
Sweetpotato Weevil: This is the most serious worldwide pest
of sweetpotatoes, however, this pest is effectively management
in commercial production areas where it occurs in the US, due
to comprehensive IPM programs that include (monitoring with
pheromone traps, field sanitation, cultural practices, clean seed
programs and the effective use of labeled insecticides). Adults
and larvae feed on foliage, but prefer stems and roots. Infested
sweetpotatoes are riddled with small holes and galleries especially
in the stem end. They turn bitter and are unfit for consumption
by either humans or livestock. Use only " seed " and
plants produced in approved and trapped weevil-free areas. All
purchased roots/plants, including those produced out-of-state,
must be certified. Use pheromone traps in plant beds, greenhouses,
and in fields to detect sweetpotato weevil. Some varietal
tolerance exists. Chemical control with weekly or biweekly
sprays is difficult. Most states with commercial production areas
of sweetpotato have strict quarantine rules in place for sweetpotato
weevil. Chemical control with biweekly or weekly sprays
can be difficult to attain depending on other factors and should
be used in conjunction with other management tools as indicated
above, in areas where the weevil does occur.
Sweetpotato Flea Beetle: Adult beetles overwinter in debris,
along fence rows, and at the edges of wooded areas. In the
spring, eggs are laid in the soil near host plants. There are several
generations per year. Adults feed on foliage leaving channels
on the upper leaf surfaces. Larvae feed on roots etching shallow,
winding, sunken trails on the surface, which enlarge, darken and
split. Monitor adults with yellow sticky cups. Control morningglories
and weeds along field margins and plow under crop debris.
Use resistant or tolerant varieties. In fields with a history of
infestation use a preplant or a side-dressed soil insecticide over
the foliage up to the last cultivation. Control adults with insecticides.
2023
Vegetable Crop Handbook for Southeastern United States
Whitefringed Beetle: Larvae feed on roots causing damage
similar to that of wireworms and white grubs. Only flightless, female
adults occur and feed at the base of plants leaving scars on
the stem. They also feed and notch leaves. They are most active
in July and August and produce eggs in groups without mating.
Avoid infested fields and rotate crops. Only grasses are not
suitable as hosts. Monitor for adults or leaf notching. Limited
control may be achieved by using tolerant varieties, foliar insecticides
applied every two weeks and soil insecticides. Record
whitefringed beetle sites and do not plant sweetpotatoes in these
locations.
Wireworms: Tobacco wireworm, southern potato wireworm,
corn wireworm leave small, irregular, shallow or deep holes in
the surface of sweetpotato roots. Larvae are identified by differences
in their last abdominal segment. Wireworm adults (click
beetles) lay their eggs in grassy, undisturbed soil. Adults feed on
weed seeds (pigweed) and corn pollen. Avoid land previously in
sod or fallow. Wireworms may be detected prior to planting using
corn, wheat, or oatmeal bait stations. If necessary, broadcast
and incorporate a preplant insecticide, or use a granular material
at root swell. Timed foliar sprays are of limited value, as adults
do not feed on sweetpotato and are only controlled when sprays
contact adults or larvae move into a treated area. Control weeds
and do not allow them to mature to seed. Avoid planting in fields
with corn wireworm. Avoid planting behind corn, grain, and
grain sorghum. Tobacco wireworm adults can be monitored with
yellow sticky cups. Wireworm adults are attracted to black-light
insect traps.
White Grubs: These can cause large, shallow, irregular damage
on the surface of sweetpotatoes. Species include Japanese beetle,
spring rose beetle, and green June beetle. Adults lay eggs in
grassy areas (also see section on wireworms). Pheromone traps
are under evaluation. Japanese beetles are attracted to traps.
White bucket traps attract spring rose beetles. Use a preplant insecticide
and foliar sprays when adults are active.
Fruit Fly: Fruit flies may be a nuisance in storage houses when
sweetpotatoes decay due to other causes such as souring, chilling,
and Rhizopus soft rot. Fruit flies feed on decaying vegetables.
Maggots may be seen in decaying roots. Fruit flies may
become established in cull piles and spread to the storage house.
They do not cause rots. Harvest, cure and store only sound
sweetpotatoes. Dispose of culls, inspect the storage house and
use traps. If necessary, spray with an appropriate insecticide.
HARVESTING AND STORAGE
A 3 to 4 month growing season is required for root development.
After the roots are dug, they should be cured in the storage house
at 80° to 85°F and 90% relative humidity for 6 to 8 days. Curing
time can be adjusted for varieties that have a propensity to
sprout quickly under curing conditions following harvest. After
curing, temperature should be lowered to 55°F, but relative humidity
should be maintained at 85%. Temperature should never
go below 55°F or chilling injury may result, depending on length
of exposure. Above 60°F, sprouting will occur and root weight
decrease. See Table 14 for further postharvest information.
109
Southeastern U.S. Vegetable Crop Handbook - 2023

Table of Contents for the Digital Edition of Southeastern U.S. Vegetable Crop Handbook - 2023
