QUESTION: Even though we water our tomato plants on a regular basis the leaves have rolled up. What caused this to happen? We fear they may be infected with some kind of blight.
ANSWER: Leaf roll on tomatoes is a fairly common occurrence. The leaflets of older leaves roll upward along the edges and curl around the mid-vein. The leaves have a normal green color and are firm and leathery to the touch. Eventually most of the leaves will be affected.
Tomato leaves curling, especially those near the top of the plants, do not indicate the so-called curly top disease of tomatoes that is frequently discussed in various garden publications. This virus disease, which causes only leaf symptoms, is extremely rare in Western Washington. More than likely, the curling leaves on your tomato plants are caused by physiological stress brought on by drought. The cool nights and warm, sunny days that are common this time of the year may be a contributing factor. The curling symptoms are nothing to worry about. It does not damage the fruit and will usually disappear with proper watering practices which prevent plants from getting too dry.
QUESTION: We have discovered a bee's nest in one of our rhododendrons. Should we spray it or just leave it?
ANSWER: Both yellow jackets and wasps are beneficial; they prey upon flies, caterpillars and other insects. Unfortunately they can be a potential health hazard to people allergic to their stings and simply painful to others who are not allergic. If nests are constructed in out-of-the-way locations, they should be left alone because they do help to manage other pestilent insects. If however, the nests are located in areas where there is a danger of human interaction, they should be removed. Yellow jackets can be easily controlled with a ready-to-use powder formulation of carbaryl (Sevin) that is placed or puffed into the colony entrance. Wasps can be easily managed using one of the several insecticidal aerosol products specifically designed for this purpose. Use extreme caution around the nests and follow all product directions.
QUESTION: We have several trees in our landscape that don't look healthy. They have a thinning canopy and premature leaf drop. They do not have any visible disease or insect problems. Is there anything we can do to help these trees regain their vigor?
ANSWER: Trees in decline have an unthrifty look to them. Often leaves are fewer than normal, and overall growth has been poor. Internode length (the space between each year's twig bud scars) decreases from several inches to less than 0.5 inch. Leaves may have yellow or brown margins, and tips may be smaller than normal. There may be premature autumn coloration and early leaf drop. Twigs at the ends of branches may die back, and often limbs at the top of the tree will be drying and bare of leaves. Dead branches can occur next to apparently healthy branches.
Tree decline never happens overnight. Decline can be the result of a single disease or environmental event or, more common, from stress over many years. Injury to the trunk, injury to the roots or injury to the whole plant may all contribute to tree decline. Insufficient water over several years is the most common cause of tree decline. Trees need supplemental irrigation in the dry summer season even if the spring has been wet. Irrigation is particularly important for trees transplanted in the past three years.
Water deeply and infrequently (once a week) rather than sprinkling lightly for 5 or 10 minutes a day. When the soil 4 inches below the surface feels dry or only slightly damp, it is time to water. Well-drained sandy soils need more water more often than a loam or clay soil.
Identify sources of stress and eliminate them if possible. Mulch under the tree to keep down weeds and to prevent both mower and weed eater damage to the trunk. Organic mulches such as leaf litter and wood and bark chips work well. Do not use plastic because it interferes with root-soil gas exchange and water infiltration. Spread the mulch 3 to 6 inches deep in a circle at least three feet in radius from the trunk. Keep the mulch from direct contact with the tree trunk.
EDITOR'S NOTE: For answers to local gardening questions, contact Master Gardener Rachel Gana at 642-8723 or e-mail her at: email@example.com.