Diagnosing plant problems
By Ray Ridlen
Some general guidelines are helpful when attempting to diagnose plant problems.
First, try to identify the plant, which will greatly narrow the problem possibilities.
Next, identify the symptoms. Each plant will have its own characteristic symptoms. Learn to recognize them.
Insects—Visible damage to stems, flowers and especially leaves. Check closely. Type of damage varies with insect. Leaves may be chewed, mottled, or cupped.
Diseases—Plant tissue, especially leaves, deteriorated, or with dead spots or covered with powdery growth.
Fertility and pH—Plant growth not vigorous. Two most common causes are:
Pale green leaves, lower leaves first–nitrogen deficiency; and
Yellow leaves, usually with dark green veins, newest leaves first–iron deficiency.
Nematodes—Plant growth not vigorous. Leaves are normal shape and color, but do not develop rapidly. Root growth is poor, galls or swelling often present on root system.
Root damage—Plant growth is not vigorous. Leaves may wilt even though soil is moist. Brown, “scorched” margins may develop around leaves. Leaves may turn yellow and drop, generally affecting all leaves. Causes include: excess fertilizer, over-watering, grub worms, mechanical injury, and an addition of excessive fill soil.
Weed killer damage—Erratic, distorted growth (new tissue only), or burning of existing tissue. Generally occurs within one to two weeks after herbicide application, but can be up to six to eight weeks.
Transplanting shock—Plant fails to leaf out and grow normally. New growth lacks vigor and leaves are much smaller than normal, especially with large plants. Will persist one to four growing seasons after transplanting.
Miscellaneous growth problem—Plant grows well for a short period of time, then has problems. Growth may become scorched, lanky or otherwise affected. Common causes are excessive shade or sunlight, overcrowding, under-watering, use of varieties poorly adapted to area.
Remember that black discoloration and rotting on the bottom of tomatoes is blossom-end-rot. It is not caused by disease or insect and no spray will provide a cure. Mulching the soil surface to maintain more uniform soil moisture will help as much as anything.
Squash that turns dark and shrivels is caused by incomplete pollination of the female flowers. Spread pollen from flower to flower every other day with an artist’s brush.
High temperatures can cause tomato blossoms to fall without producing fruit.
Diagnosing plant disorders is easier said than done. Perhaps these guidelines may enable a more qualified do-it-yourself diagnosis.