Pests in the July Garden
Posted: July 11, 2012
Summer’s here and so are the pests. What is your plant suffering from and how should you take care of it? Here are some common problems facing our gardens in July.
Aphids are seen on most plants, from herbaceous to hardwoods, at various times of the year. These little guys can really be pesky. In colors of green, black and red, these soft bodied insects will suck the juices right out of a plant. The good news is they are relatively easy to control. Spraying a hard stream of water will knock them down. Most oils and soaps will do the job too. Keep an eye out for these insects as well as the beneficial insects that feed on them. Lady beetles are great devourers of aphids, at both the lady beetle’s larval and adult stages. Get to know what they look like so if you see a larvae lady beetle, you’ll know that the aphids are already being taken care of.
Blossom end rot on tomatoes and peppers is a common problem and often thought of as a disease. Samples of this come into the Extension Office on a regular basis beginning the end of June. The symptoms of this problem look like a leathery black end on the tomato. On peppers, it’s often found on the side of the fruit. It’s particularly exacerbating to find this problem because you typically don’t see it until you are ready to harvest. The tops of the fruit look ripe and delicious; then, bam! the bottoms are black.
This problem is not a disease, virus, or insect problem, but rather a nutritional issue. Calcium is a nutrient provided by the soil. Calcium helps the cell walls in the fruit to form. It moves through the plant by water. In the soil, it becomes even less accessible to the plant if the soil pH is less than 5.8. When the plant is young, it uses less calcium. As the fruit begins to grow, more calcium is needed for the fruit to develop into a ripe tomato. Since the calcium is moved by water, and the fruit of a tomato or pepper plant becomes mature during the heat of the summer, more water is needed to allow more calcium to be available to the fruit. Hence, if you are not watering regularly during drier times, blossom end rot occurs.
So what should you do? With the understanding of why tomatoes and peppers get blossom end rot, the solution is simple. Watering regularly during time of fruit development - approximately one inch per week - and adding calcitic lime to the soil if the pH is under 5.8 will help insure a healthy tomato or pepper. If the problem occurs, your best solution is to pick the fruit that is affected and begin watering regularly.
Powdery mildew is a disease often found on lilacs, bee balm, and garden phlox as well as other ornamentals. This disease begins to grow under high humidity when temperatures are between 60 and 80 degrees. Typically, powdery mildew is not fatal to a plant, but it can cause deformity and yellowing of the leaves as well as early leaf drop. Good air circulation is critical in controlling or deterring the disease from developing. Planting where the plants are not against a wall or fence and not crowded by other plants will help in the control of this disease. As leaves drop, good sanitation becomes very important for control of additional spore dispersal. Pick up the leaves and discard. Reduce as many of the infected leaves and stems as you can to help control the problem. If additional control is warranted, fungicides can be used as soon as the mildew is detected. Following the label on the fungicide for appropriate use and frequency will help control the problem.
Spider mites become a problem now as their damage typically shows up in the heat of the summer. Did you ever see dwarf Alberta spruces suddenly turn brown about this time of year? Needles drop, and the plant appears to be dying. These symptoms point to the spruce spider mite. Even though the evidence of the mite appears in the summer, the actual feeding happens in the spring and fall in cooler temperatures. Activity occurs when the daytime temperatures are between 60 – 70 degrees. The Spruce spider mite not only feeds on the Dwarf Alberta Spruce but also can be found on hemlocks, other spruce, arborvitae, junipers and firs.
So how does one control this deadly trouble-maker? Unfortunately, by the time you see the damage caused by this pest in the summer, it’s too late to do much about it. When the temperatures start to rise above 80 degrees, they become inactive and the populations begin to decline due to predatory activity. When temperatures reach 90 degrees, adults will lay eggs and go into dormancy.
Since the feeding activity happens in the cooler temperatures of the spring and fall, that is the best time for control. Spraying with an insecticidal soap or oil spray will help control this little pest. Good coverage is important when using these pesticides, but be sure to read the label for temperature needs and direction for mixing. Also note that if you are having trouble with the spider mite on blue spruce, spraying with oil or soaps will take away the blue coloration, so it is not recommended for those types of plants.
July is often the time when people begin to see cone-like growths on spruce trees. These are spruce galls. There are two kinds: the Cooley spruce gall and the Eastern spruce gall. Both have very specific life cycles but are managed very similarly.
The Cooley Spruce Gall pest requires both the spruce and the Douglas fir as hosts. To complete their very complicated life cycles, the insects can begin on the spruce but must have a Douglas fir to fly to in order to complete the five stages of their life cycle. They feed on the new buds, lay eggs, then during a very long life cycle of traveling to the Douglas fir and back, many stages take place, continuing for two years. The galls will often destroy the shape of the spruce, since it’s the terminal buds that are affected. On the Douglas fir, the symptoms are not as evident. Yellow spots on the needles, which in heavy infestation can change the overall coloration of the tree, are the symptoms. Typically, you’ll see these galls on the Colorado blue spruce, but they can also be found on all spruce.
The Eastern spruce gall is not as complicated. Typically, it is found on the Norway spruce, but it can be seen on white or red spruce as well. This gall looks similar; however, it does not need a host plant to complete its life cycle and only takes one year to complete its life cycle.
For both of these galls, the same control is recommended. Cutting the galls off when they are green will control the problem. If the trees are too large, or there are too many galls to cut, using the systemic insecticide imidicloprid in the fall of the year will help control the pest. Horticultural oil is also a recommended control; however, not on blue spruce or any other spruce that has coloration you want to maintain.
By the end of July through August, we see a lot of tulip tree (Liriodendron tulipifera) samples come in. Typical symptoms are blackening leaves and a sticky substance on the leaves that drips onto cars, sidewalks and driveways. Upon closer inspection, clients may see bumps on the stems of the tree. The blackening on the leaves is sooty mold, which grows as a result of the secretions of the growing scale which feeds on the tree. The insect infestation may lead to quick decline of the tree. The insect sucks plant fluid from the tree, and the sooty mold reduces leaf surface, thus interfering with photosynthesis, an important process for plant growth and health.
Control for this insect is best done in the early spring using a dormant oil spray. This will control the overwintering nymphs, thus reducing the amount of insects that will feed in late summer. However, control can be done with the oil in mid-August through mid-September. This will control the newly emerged crawlers that would have hatched from the adults. Once the insects enter the adult stage, they become more difficult to control due to the shield, or scale, they develop. When using pesticides, be sure to read the label for instruction.
Understanding pests, their life cycles and what they feed on, will help in your choice of controls and when that control should be applied. Be sure to have the problem identified correctly and make your decision from the facts. Gardening is full of challenges and rewards. Take the time and learn more about all aspects of the garden and enjoy. Whenever using pesticides, be sure to carefully read the label.
Where trade names appear, no discrimination is intended, and no endorsement by Penn State Cooperative Extension is implied.
Mary Ann Ryan is the Consumer Horticulture/Master Gardener Coordinator for Penn State Extension in Adams County. Penn State in Adams County is located at 670 Old Harrisburg Road, Gettysburg, PA 17325; phone 334-6271.