Editor’s note: Kelly R. Jackson takes questions called into his phone recently at the Christian County Extension Office and answers them in the Garden Corner column.
Question. My blackberries have white spots on the fruit. What is causing that?
Answer. The fruit of a blackberry and raspberry is called an aggregate fruit which is made up of many smaller fruits called druplets. This season some have found their blackberry fruits to have white or tannish colored druplets causing the fruit to look diseased. A specific reason for this syndrome has not been determined but several explanations have been proposed.
The most common cause is thought to be solar injury (sunscald) due to UV radiation. Varieties vary in susceptibility to sunscald. Sunscald seems to be worse after an abrupt increase in temperatures accompanied by a drop in humidity, especially when wind is present. Hot, dry air allows more direct UV rays to reach the fruit. ‘Apache’ and ‘Kiowa’ blackberry and ‘Caroline’ red raspberry appear to have the syndrome more frequently.
Other possibilities may include stinkbug damage or red berry mite feeding damage but evidence of the pest should be present.
Q. My spruce is losing its needles. What is causing this?
A. Blue spruce and Norway spruce are popular landscape plants in Kentucky. However, many factors can cause spruce trees to cast (shed) needles. Casting may be the result of environmental stresses (heavy soil, poor drainage) or fungal diseases. In Kentucky, Rhizosphaera needle cast is the most common disease of spruce. This disease causes needle drop on lower branches, resulting in a distinct thinned appearance. Stigmina needle cast is a less common disease of spruce, but also causes symptoms similar to Rhizosphaera needle cast. Management options for both diseases include reduction of plant stress, good sanitation practices, and timely use of fungicides. Symptoms become evident in summer when needles on lower branches turn purplish or brown. Needles fall within a few weeks and lower limbs are left bare.
In order to determine whether Rhizosphaera or Stigmina needle cast is present, infected needles should be inspected with a hand lens. Look closely for the type of fungal fruiting body emerging from stomata (pores in needles) to confirm diagnosis. Rhizosphaera needle cast has small, dark fruiting bodies appearing as tiny raised, grayish bumps topped with white waxy caps. While most easily recognized with a hand lens, they may also be visible with the naked eye. Stigmina needle cast has fungal fruiting structures which appear as tiny, brown to black, brush-like tufts emerging from needles.
If defoliation occurs over 3 to 4 consecutive years, branch death is likely. Stressed trees are more susceptible to infection than healthy plants, so take steps to maintain plant vigor. Properly space plants to improve air circulation, thereby encouraging rapid drying of needles. Homeowners can apply fungicides that contain chlorothalonil, copper, or mancozeb during needle emergence (mid-April). During rainy seasons or in plantings with a history of disease, fungicides may be applied 2 consecutive years during spring when fungi are most active.
Kelly R. Jackson is the Christian County Extension Agent for horticulture. He can be reached at 270-886-6328 or visit Christian County Horticulture online at www.christiancountyextension.com.