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Post-harvest insect pest management in small fruit crops

Douglas G. Pfeiffer, Department of Entomology, Virginia Tech  


When the fruit are in, it is easy to think about putting the sprayer away.  But sometimes there are insect issues that can be addressed in post-harvest, fall or winter periods.  Let’s take up a few now. 

Grape 

In general, it is advisable to maintain healthy foliage as long as possible into the fall.  Here are some insect problems that can be addressed to help achieve this goal. 

Grape mealybug and some related mealybug species can be found feeding on grapevines during much of the year.  The phloem-feeding insects are covered with white, waxy material that often is produced into finger-like projections along the sides of the body, and into long white filaments from the hind end (all of these disappear if an impressive looking mealybug is dropped into a vial of alcohol!).  Grape mealybug is a pest that can be addressed either early in the year (the recommended timing in our southeastern regional recommendations, https://smallfruits.org/ipm-production-guides/), or in the fall.  Traditionally, mealybugs should be controlled if there were high populations in the fall – honeydew and sooty mold can cover foliage and clusters, and high populations can cause clusters to drop.  The situation has been made worse by the advent of grapevine leafroll virus which is transmitted by mealybugs.  Mealybugs can be targets of natural enemies, but broad-spectrum sprays can induce outbreaks of these insects.  Venom, Assail, Actara (thiamethoxam), Admire Pro (imidacloprid), Belay (clothianidin), Applaud (buprofezin) and Movento (spirotetramat) are good candidates for chemical control of mealybugs.  All but the last two are neonicotinoids. 

Fig. 1.  A young grape mealybug on a Virginia grapevine. 

The question occasionally arises about the utility of oil sprays to grapevines in the dormant period – these have long been used in orchards.  A usual target for oil sprays is European red mite, which overwinters as eggs on the bark of fruit trees and grapevines.  On the relatively smooth bark of apple and peach branches, a coating of oil acts to suffocate the eggs (especially if applied close to hatch, when oxygen needs are greatest).  However, the shaggy bark of grapevine trunks makes it difficult to achieve adequate coverage of the eggs with an oil spray.  Another insect that may be targeted by oil sprays is grapevine scale.  Vines may develop populations of scales especially if broad spectrum sprays have suppressed populations of parasitoids.  On tree fruits, aphids are also the targets of oil sprays since they overwinter as eggs on the bark.  But the main aphid on grape uses black haw as its winter host, so aphid management in vineyards does not benefit from oil sprays. 

Fig. 2. Grapevine scales on a Virginia grapevine.  The large individuals are the scale coverings of mature females, and the small, white individuals are settled crawlers. 

General examination of vines. Vines may be examined in the post-harvest period for symptoms of Pierce’s disease, including typical leaf discoloration and the presence of matchstick petioles.  Unusual pest situations may also be revealed, such as lecanium scales.  European fruit lecanium and terrapin scape could occur on grapevines but this is not common. 

Caneberry 

Rednecked cane borer is a member of the flatheaded borer family Buprestidae.  The elytra are black or dark grey, and with a distinctive copper-colored pronotum.  The adult beetle is about a quarter inch long.  Adults are around for a good part of the season, from May to August.  Larvae make spiral tunnels under the bark, reducing growth of the plant.  When sprays are made for this insect, the target is ovipositing females.  During winter pruning, assess the presence of galls.  If more than 10% of canes have galls, a chemical control approach is needed in the coming season.  But pruning during the dormant period can help reduce populations.  Removal via pruning is most effective if wild brambles growing nearby are also removed.  Removal of galled canes can be helpful at other times of the season as well. 

Fig. 3. Rednecked cane borer adult and galls.  Susan Ellis, James Solomon, Bugwood.org. 

Raspberry crown borer is a clearwing moth (Sesiidae).  Moths in this family are often wasp mimics, and this one is a good mimic of a yellowjacket. Crown borers invade the crown of the plant where they can cause girdling.  After the eggs hatch, the larvae spend the winter in hibernacula beneath the soil surface.  During the first summer, larvae feed within the crown; in the second summer, they tunnel upward into canes.  They may be controlled by a soil drench in the fall, while they are preparing for overwintering, or in April, before they tunnel into the plant.  Brigade (bifenthrin) or Altacor (chlorantraniliprole) may be used, applied in a minimum of 50 gallons of water per acre.  In addition, infested plant may be rogued out. 

Fig. 4. Raspberry crown borer and larvae in its gallery.  Univ. Georgia, Bugwood.org.
Fig. 4. Raspberry crown borer and larvae in its gallery.  Univ. Georgia, Bugwood.org.

Rose scale may occasionally develop on caneberries.  Rose scale overwinters as eggs beneath the maternal scale covering.  There are 2-3 generations in the north, but more in the south.  This scale can be controlled during the dormant or delayed dormant period using Admire Pro (imidacloprid), Brigade (bifenthrin) or a 2% solution of Tri-Tek oil.  Sprays should be made when temperatures are above 50 degrees F. 

Fig. 5. Rose scale infestation in a caneberry planting in Blackstone Virginia. 

If high populations of aphids, mites or leafhoppers are present after harvest, they can be controlled as during the pre-harvest period. 

Strawberry 

Since strawberries are harvested early, for perennial or matted-row crops much of the remaining season is a post-harvest season.  Foliar feeding pests can be controlled as normal.  A couple of pests bear specific mention. 

Strawberry root weevil mainly occurs in beds that are in place for several years, but not in beds that have a shorter lifespan.  The adults (all females) are flightless, and since they have to walk into the planting, and only have a single generation, populations need some time to build.  If root weevils need to be controlled, Brigade (bifenthrin) or malathion may be applied when leaf-feeding by adults appears. 

Fig. 6. Strawberry root weevil adult. Whitney Cranshaw, Bugwood.org 

White grubs may be a problem in strawberries, and Admire Pro can be applied at renovation, when it is incorporated into the soil. 

Blueberry 

Blueberry bud mite is a tiny mite in the rust or blister mite family (Eriophyidae).  Mites in this family tend to be highly host specific, and blueberry is the only host. The mite invades flower buds in late summer and fall, where they feed during the winter.  Attacked buds fail to expand and bloom, or give rise to malformed, roughened fruit.  The biology of this pest is not well known.  Treatments may be considered in blocks of susceptible varieties with a history of infestation.  High volume and high-pressure applications of horticultural oil may be made.  Summer topping and hedging right after harvest helps remove older, infested tissue and can help in blueberry bud mite management. 

Scale insects, while not usually a problem on blueberries, may be exacerbated by broad spectrum sprays for SWD or blueberry bud mite.  They can be managed with applications of Sivanto Prime (flupyradifurone) or Movento (spirotetramat). 

So, after harvest, look through your plantings and assess insect populations, and determine whether any action is needed.  This may be a valuable time to take care of issues!