Time to Control Fruit Diseases

Winter is a good time to prepare fruiting crops for the season ahead. Many fruit diseases can be partially controlled by being vigilant with cleanup and fungicidal sprays at proper times. Remember that pruning should take place in late February on fruiting trees. Below is a list of fruit crops along with diseases of concern and some things to do to help you have a successful harvest.apple-tree-429213_1920

Apple diseases of concern: scab, cedar rust, and fire blight.

  • If you are ordering nursery stock, plan on growing disease-resistant apples. Nursery catalogs will indicate varieties that are scab-resistant.
  • Prune out old fire blight cankers now, while it is still cold, so new infections won’t occur. Prune also to thin the tree canopy to allow good air movement and sunlight penetration.
  • Remove and destroy fruit mummies left on the tree from last season. Remove nearby cedar trees, source of rust diseases, if possible.
  • Obtain fixed copper or Bordeaux mixture to apply to the apple twigs and branches just as the buds begin to swell next month.
  • Obtain a scab fungicide with ingredients such as mancozeb, captan, myclobutanil, or thiophanate-methyl so that sprays can be applied as green foliage (green tips) is just emerging and repeated periodically throughout the spring months. Carefully read fungicide labels before making spray applications.

Stone fruit diseases of concern: peach leaf curl, plum black knot, and eventually brown rot and scab.

  • Apply fixed copper or Chlorothalonil sprays now to prevent peach leaf curl. In some parts of the state, it may be already too late because of warm weather, buds may have begun to swell and leaf curl infections may have just begun.
  • Prune to thin the tree canopy to allow good air movement and sunlight penetration. Prune out any diseased or cankered twigs and branches from the trees. Prune out black knot disease swellings from plum trees.
  • Remove and destroy last year’s mummified fruit still hanging in the tree or on the ground.
  • Obtain brown rot and scab fungicides with ingredients such as sulfur, captan, or myclobutanil. Read and understand the chemical labels.

Grape diseases of concern: black rot, anthracnose, cane and leaf spot, and downy mildew.

  • Prune the grape canopy to allow good sunlight penetration and air movement, as well as to maximize fruit production. Prune out any diseased, dead, or cankered vines.
  • Remove and destroy all of last year’s fruit mummies hanging on the vine and lying on the ground.
  • Apply lime-sulfur sprays to the dormant vines just as buds begin to swell to prevent anthracnose.
  • Obtain fungicides with ingredients such as captan, mancozeb, myclobutanil, or thiophanate-methyl to be used for black rot and cane and leaf spot management. Be prepared to apply fungicides as the first green leaves are beginning to appear on the vines and to repeat the applications throughout the spring as called for on the pesticide label.

Bramble diseases of concern: anthracnose and orange rust.

  • Prune out dead and winter-injured canes.
  • Apply lime-sulfur fungicide to the canes in early spring just as the buds begin to swell, but before green tissue emerges.
  • Be prepared to remove and destroy orange-rust infected blackberries and black raspberries. These plants will appear abnormally whitish and spindly in early spring as they emerge from the ground. If orange rust is present in the neighborhood, remove and destroy wild blackberries growing in nearby fields and fencerows, if feasible.
  • If, because of rainy weather last year, plants died from root rot disease, improve drainage in the garden or grow brambles on raised beds.

Strawberry diseases of concern: fruit rot diseases.

  • Apply straw mulch to the beds between the rows and under the canopy so that fruits will not have to touch the ground.
  • Provide adequate spacing of the strawberry plants to provide good sunlight penetration and air movement to help reduce gray mold fruit rot.
  • Hand remove dead leaves and stems from the strawberry bed to reduce the presence of the gray mold fungus.
  • If sprays, such as captan, are to be used to prevent fruit rot, the sprays need to be applied to the strawberry flowers in early spring.

Blueberry diseases of concern: twig blights and cankers.

  • Prevent twig canker diseases by avoiding stressful growing conditions. Mulch blueberries with organic matter, such as wood chips, and adjust the soil pH if necessary to provide favorable growing conditions.
  • Prune out dead and dying twigs and branches from the blueberry plants.
  • If, because of wet weather, blueberries are declining and dying due to root rot disease, improve garden soil drainage or grow blueberries on raised beds.

Submitted by Dennis Morgeson, Agent for Horticulture, Washington Co. Cooperative Extension