Tidewater Gardening - July 2013

Pests and Problems in July

by

K. Marc Teffeau

We are now in the active gardening season. The cool, somewhat wet spring has passed and we are now busy harvesting our gardens and maintaining the landscape. Now is the time to watch out for those seasonal pests.
The hot dry weather in July brings out red spider mites on many ornamental plants. Inspect roses, evergreens and marigolds in particular, for pale green leaf color. Since spider mites are so small, the easiest way to determine if they are causing problems with your plants is to do the paper test.
Hold a white sheet of paper underneath a leaf and briskly tap it. Tiny, crawling mites will drop onto the paper if they are present on the leaf. If you take your finger and squash the mite, it will leave a red streak on the paper.
If the infestation is light, discourage mites with a forceful, direct spray of water aimed at the underside of the leaves. Mild to heavy infestations can be controlled by spraying the plants with a summer horticultural oil, horticultural soap, or a miticide. Severely infested annual plants should be removed and destroyed.
Japanese beetles are also showing up now. A non-chemical method of reducing their damage is to remove all flower blossoms as soon as they begin to fade and all fruit as soon as it is ripe. Japanese beetles are especially fond of over-ripe fruit and deteriorating flower blossoms.
After taking these preventative steps, go out to your garden daily and knock the insects off their perches and into a wide-mouthed jar soapy water. That will gum them up and prevent them from flying away.
It is important to remember that if you do apply an insecticide or fungicide to plants during the summer, it is usually a good idea to water your plants several hours before spraying them, especially during dry weather. Drought stressed plants have less water in their tissues. As a result, chemicals that enter the leaves will be more concentrated and may burn the leaves.
The best time to spray is in the early morning when the temperatures are lower. When temperatures go above 85° you run the risk of burning the plants with pesticide sprays. Many times it is not the pesticide itself but the carrier, which is usually solvent or oil based, that does the damage.
As with doctors, the first rule is “do not harm” ~ the same practice should be put into place in the garden. During periods of very hot, dry weather, sometimes the best course of action is to do nothing. Don’t prune, apply fertilizer or spray the plants. Plants compensate for stress by relative inactivity. Cultural practices which encourage growth, instead of being beneficial, can induce further stress.
If you are one of the many homeowners who have jumped on the bandwagon of container gardening, you are likely to have a container or two of vegetables or flowers on the patio or porch. Container grown vegetables and flowers can dry out quickly, however, especially if they are on a deck or concrete patio in full sun. Daily watering may be necessary.
Apply water until it runs out the drainage holes. Clay pots permit additional evaporation from the sides and watering must be done more often than when plastic pots are used. Small pots also dry out faster than larger planters. Feel the soil in containers at least once a day and twice on hot, dry days to be certain that the plants are getting enough water.
During periods of extremely hot weather, it may be advisable to move the containers to a cooler spot or shade them during the hottest part of the day. Sunlight reflected from the concrete or pavement can raise the temperature of the container 20 to 30 degrees warmer than the air temperature.
Also, watch the weather report for prediction of severe afternoon or evening thunderstorms and prepare to move the container to a more sheltered location, if possible, during heavy rain or wind storms.
Don’t forget about the vegetable garden. Continue to make successive plantings of green beans, beets, and sweet corn (early maturing varieties) throughout the month of July. For a fall harvest of cabbage, broccoli, cauliflower and Brussels sprouts, set transplants in late July. For a fall harvest of lettuce, radishes, turnips, kale and spinach, sow seeds in late July to early August.
Remember that in the summer, dry conditions may make working the soil difficult and inhibit seed germination. Plant your fall vegetables when the soil is moist after a rain, or water the area thoroughly the day before you plant. Seeds may be planted in a shallow trench to conserve moisture. Cover the seed about twice as deeply as you do in the spring. Early maturing varieties are best for late planting.
If you are growing vine crops like cucumbers you can stop vine crops from taking over your garden or lawn by pinching off the fuzzy growing tips. This also directs the plant’s energy into ripening fruit rather than producing more vine.
When I was the county extension agent in Talbot a few years back, homeowners would come into the office with samples of funky looking tomatoes and ask what was the problem. Well, there are a couple of environmental factors that cause problems in tomatoes during the summer. Temperature and water may cause abnormalities in the fruit.
The most common disorder is blossom end rot. It is caused by the interaction of several factors, primarily the water supply and a calcium imbalance. A small water-soaked spot forms near the blossom end of the fruit. It then becomes dark, leathery and sunken. The affected area may vary from a small spot to over half of the fruit.
This problem always stressed out the gardener because he or she was eyeing harvesting the first tomatoes of the plant. Blossom end rot is more of a problem on the first fruit set and is most severe when periods of hot, dry weather following periods of excessive rainfall. Certain varieties of tomatoes seems to be more prone to blossom end rot.
Cultural practices that may reduce this problem include making sure that your soil pH is correct and that enough calcium is present. Incorporate compost into to the soil to improve water retention. Mulch to conserve soil moisture, and to moderate fluctuations in soil temperate and moisture loss.
Cat-facing is a disorder that results in malformed fruit which have deep indentations and cavities extending into the blossom end, and brown scar tissue in bands between the lobes. This condition results from interference in the normal fruit development. These include low temperatures (below 55°) at flowering, excessive nitrogen fertilizer and herbicide damage.
Tomatoes transplanted before warm weather are more likely to produce cat-faced fruit. To reduce cat-facing problems, avoid the use of any 2,4-d herbicides near the garden, don’t transplant early and use minimal nitrogen fertilizer until the third cluster of fruit has formed. Discard all cat-faced fruit.
While we are talking about vegetables, start your broccoli, cabbage, and cauliflower seeds now so you can set them out as fall transplants in August. It is difficult to locate fall vegetable transplants in this area as most greenhouse growers are oriented to the spring season.
Mid- to late July is a good time to direct seed lettuce, spinach, beets, carrots and turnips into the garden. They may be a little slow in germinating because of the high temperatures. Try lowering the soil temperatures by covering the seed bed with a floating row cover like “re-may” or some other shading material.
Succession plantings of green beans can go in until the first of August. Wait until August for the fall planting of peas.
On the flower side, the annuals in the landscape in mid to late July usually start to fade. You can rejuvenate them by cutting them back to approximately half their height, then fertilize them with a liquid fertilizer and apply a 1- to 2-inch layer of mulch.
For any annuals that didn’t make it, remove them and add them to the compost pile. You can replant beds with hardy annuals or perennials such as pansies, calendulas, globe thistles, or sea pinks. Pinch back snapdragons after blooming to promote a second flush of flowering.
July is the time when your bearded iris should be divided and replanted. Dig them up carefully and throw out the diseased and borer-infested rhizomes. Separate the rhizomes and dust the cut ends with sulfur to reduce potential rot problems. Discard the old center portion and plant with the top of the rhizome barely showing above the ground. Cut the leaves or “fans” back to 8 inches.
If you want to keep some geraniums over the winter, cuttings should be made in late July to start plants for winter and spring indoor bloom. To make the cuttings, use the tip of branches about four inches long. Cut off the bottom leaves and stick the cuttings about 1/3 of their length in a moist sand-peat mixture. Roots will develop rapidly and new plants should be ready for potting in about four weeks.
When pruning away twiggy young growth from rose bushes, make use of the prunings by rooting them and producing new plants. Treat stem bases with a rooting hormone, stick them in soil in a cold frame that is out of the sun, and water them well. If some die before rooting ~ no great loss ~ just toss them into the compost pile.
Holly, azalea, and camellia cuttings can also be rooted in a sand-peat moss mixture set in a cool, shady location.
July is the time when many retail garden outlets use a mid-summer clearance sale to rid their yards of plants left over from the spring sale season. In properly managed sales yards, when plants have been watered and fertilized and where insects and diseases have been controlled, plants are still in good condition. They will tolerate transplanting at this time of the year providing that they are balled and burlaped or container grown.
Do not attempt to transplant bare-root plant material now. Be careful about buying clearance plants where the sale of plants is a side income source. Most of the time, little attention has been paid to the proper care of this material while on the lot. When selecting sale plants under these conditions, make certain that the plants are alive. Regardless of what the sales clerk tells you, horticultural scientists have not discovered a method of reviving dead plants.
Happy gardening!

Marc Teffeau retired as the Director of Research and Regulatory Affairs at the American Nursery and Landscape Association in Washington, D.C. and he now lives in Georgia with his wife, Linda.