Insects can be so cute and colorful or dark and creepy. No matter which category they fall into, growers would rather not see most of them unless they are beneficial. For growers, pests are pests, and it’s the grower’s job to control them. Following are a few of concern:
Strawberry crown borer
The strawberry crown borer is a stubborn pest. Legless, creamy white larvae bore into the plant crown, according to Thomas Kuhar, a vegetable entomology Extension specialist and professor; and Douglas Pfeiffer, a fruit entomologist, associate program director and professor, both at Virginia Tech. This insect will bore so much that its feeding hollows out the crown, leaving the plant to possibly die.
According to Kuhar and Pfeiffer, the adult crown borer will feed on the plant’s leaves and chew holes in the crown. Adults also may drop eggs in the crown. One adult generation per year will overwinter then start moving again when the strawberry plants blossom.
The adults appear dark brown and are flightless snout beetles about 4 mm in length with three darker spots on each wing, according to Kuhar and Pfeiffer.
To control the strawberry crown borer, they advise rotating strawberry crops, and avoiding planting them no greater than 300 yards from older plantings. Plan to deeply plow and compact the soil to destroy much of the hibernating weevils.
Strawberry root weevil
Root weevils can feed on young strawberry plant roots and crowns, according to Ric Bessin, an Extension entomologist and professor at the University of Kentucky. Grubs create very damaging tunneling in the roots and crowns. Results are stunted and darkened colored roots and crowns, and the leaves will become bunched together. Damage can weaken or even kill strawberry plants. Adult root weevils can eat notches in the leaves, but their damage usually isn’t as severe as the grubs, Bessin noted.
Adult root weevils are small beetles with a dark snout, Bessin said. They can sport rows of pits on their backs. Root weevil species may appear different in color and size. For instance, some are black to light brown and are about 1/5-inch. Others are chocolate brown and can only grow to ¼-inch. Others may look black and have small flecks of yellow along their back. These can grow to 1/4-inch.
Grub root weevils range in size from 1/4-inch to 1/2-inch long, according to Bessin. Their body shape may look like the letter “C.” These grubs are small and legless and may have a light-colored head. Grubs will overwinter in the soil and pupate in the spring. Once the adults emerge, they feed at night on the strawberry plant foliage and leave notches on the leaves. From 10 to 60 days (depending on the root weevil species), he said the adults begin to lay eggs in the soil near the plant. Once the eggs hatch, grubs begin feeding on the roots.
To help control or spread root weevils, Bessin advises plowing under old strawberry beds immediately after the season is over. He also advises foliar spraying post-harvest to control adult root weevils before they lay their eggs. Growers can beware of adult leaf notching, which means the insects have emerged from the soil.
Strawberry bud weevil
The strawberry bud weevil is a yield killer. According to Kuhar and Pfeiffer, damage by this pest can cause a 50- to 100-percent loss in yield. It causes damage nationwide.
The tiny larvae are grubs that appear as a creamy-white color, according to Kuhar and Pfeiffer. These insects like to hang out in unopened flower buds where they will develop in the severed buds. They reach maturity in three to four weeks. Eventually, adults will emerge and feed on the flower pollen.
The adult is chestnut brown with two black spots on its back, according to Kuhar and Pfeiffer. After overwintering from wooded areas, adults will emerge early in the growing season and quickly go straight to strawberry fields. The females will use their long beaks to puncture any unopened buds. There, they will drop an egg. Unfortunately, they damage or sever the bud, causing it to either hang from the stem or drop to the ground.
To help control the bud weevil, they advise growers to scout fields regularly, checking the plants for weevils during the early blossom or bud stage. Losses can occur once one female beetle is spotted per 40-row feet. Growers can treat when they see an average of 0.6 clipped buds per row foot. Early-fruiting varieties seem more susceptible than later-fruiting varieties.
It is wise to top plants and remove foliage and mulch soon after harvesting, Kuhar and Pfeiffer suggest. Growers also can treat to kill overwintering adults. These entomologists recommend avoiding planting near wooded areas to prevent overwintering adults from reaching the newly planted strawberry fields in the spring. Also, they suggest plowing any old strawberry beds after harvest to discourage adults from overwintering in mulch or full canopy beds. Rotate out of a strawberry field about every three years.
Sap beetles that feed on strawberries are small and black with flattened, oval bodies, according to Bessin. They feed on plant sap where plants are ripe, damaged or have cracked fruits. The damage causes small holes at the bottom of the strawberry, or it may appear in large sections on the side of the fruit. Also, sap beetles may spread disease organisms from berry to berry, which may cause the berries to rot.
To control sap beetles, Bessin advises to practice good sanitation by keeping fields clean of any ripe fruit. Growers may use beetle traps; however, he indicates that they may not be effective and certainly aren’t any replacement for good sanitation. Normally, growers can place these traps outside of the field, in-between field margins or in wooded areas. The traps may or may not stop beetles from entering the strawberry fields. In addition, he adds that growers can bait sap beetles with stale beer, molasses, water with yeast, vinegar and overripe fruit. Once the beetles fall into the bait, they usually drown, he said.
Bessin said sprays are available for growers to use but are often difficult to apply since the fruit is usually ready to harvest. So he advises selecting an insecticide with a short harvest interval, but spray only if necessary.
Contact your local Cooperative Extension agent or specialist for what chemicals are available, then, as with any insecticide, follow label directions.