In the past, Powdery Mildew and Zinnia were heard often in the same sentence. Today they are still used together but no longer to describe gardening troubles thanks to the new powdery mildew resistant selections of zinnia. The ‘Profusion’ series of zinnia are great compact plants that bloom all season. Available in white and bright colors like orange and cherry, these resistant annuals will add a lot of color and help attract butterflies to your garden.
Watch for Impatiens Necrotic Spot Virus (INSV) of your annuals. INSV can cause a wide range of symptoms on different host plants including stunting, brown or yellow circular spots on leaves, ring spots, black or brown stem discoloration, browning of leaf veins and yellow line patterns in leaf tissue. In celosia leaves become strapped shaped and flowers are stunted; gomphrena will show multiple ringspot lesions on leaves and stunted growth. Other known host plants include impatiens, gloxinia, cyclamen, begonia and certain vegetables. This disease is spread by the western flower thrip. Plants cannot be treated for control and must be destroyed. INSV is more common in greenhouses where annuals are grown and is therefore monitored closely by owners and inspectors. Occasionally, however a plant may make it to your landscape. If your annuals are exhibiting any of these symptoms, take a sample to your extension agent who can have it confirmed.
Fruits and Nuts:
Watch this month for Oriental fruit moth larvae, which tunnel near the end of succulent twigs of cherry and pear. The larva may tunnel in for 2 to 6 inches, and cause leaves to wilt. A single larva may attack five or more twigs before moving to the fruit. In fruit, larvae will tunnel through the side or at the stem union. In peaches they will exude a gummy sap. This gum turns to a dark blotch will be found on the fruit at harvest. Often, the later maturing the peach variety, the greater the percent of damage at the stem end. The larva often feeds around the pit of the peach. Brown rot infections can start at the entrance or exit holes of Oriental fruit moth.
A multipurpose fruit spray, consisting of an insecticide and fungicide, is your best defense against Oriental fruit moth. This combination of chemicals will give you the best control from plant bugs and plum curculio on peach, plum and cherry and leafroller, leafminers and codling moth on apple and pear. Multipurpose fruit sprays are applied as cover sprays after bloom until a few weeks before harvest. See the label for specific application timing.
Groundcovers and Lawns:
On warm season grasses like Zoysia and Bermuda, June 1 marks your second application of nitrogen. Your goal should be to apply 4 pounds of nitrogen over the summer. Your third and fourth applications should be applied on July 15 and September 1. Phosphorus and potassium application rates are best decided after a soil test. If your test shows high or very high levels of these two nutrients you should use a nitrogen fertilizer only, such as 34-0-0. Moderate to low levels of phosphorous and potassium will require a balanced fertilizer, such as 10-10-10.
Many lawn problems can be avoided just by mowing at the correct height. Scalping lawns exposes soil to sunlight and invites weed seeds to germinate. Consistently mowing too close may also adversely affect grass roots both in development and rooting depth. This can be especially important in lawns that are not irrigated and in cool-season lawns that are less tolerant of summer heat. Reduction of roots means the plant will have less access to water and may result in a brown lawn or death. For cool-season grasses like tall fescue, set your mower to 4 inches, warm-season lawns like Zoysia and Bermuda can be mowed at 1 inch. How often you should mow is based on how fast your lawn is growing. Your goal should be not to cut more than 1/3 of the shoot growth in a single mowing. For example a bermudagrass lawn being maintained at 1 inch should be mowed when plants reach 1½ inches. For some lawns this may mean mowing more than once a week, but the results are often worth the effort.
Perennial Flowers and Vines:
Many perennials such as garden phlox, heliopsis, veronica, and echinacea will keep flowering if they are cut back after their first bloom.
Bearded irises are among the easiest and most popular perennials to grow. The “bearded” description refers to the furry strip on each of three drooping, petal-like sepals, called falls. Flowers appear on stalks in late spring to early summer above the foliage. Hundreds of color combinations exist and they are available in a wide range of heights: miniature dwarf (up to 10″), standard dwarf (10″-15″), miniature tall (15″-25″), intermediate (15″-27″), and border (28″). All bearded irises need full sun and well-drained soil. Irises grow from rhizomes and can be propagated one to two months after bloom (June-July) by breaking off rhizome shoots (with roots intact) and replanting. It is also a good ideal to cut back the foliage to one-third their length to keep your newly planted rhizomes from being pull up by the wind. Bearded iris should be planting in a well drained, compost amended bed, just under the soil’s surface and 12-18 inches apart.
Trees and Shrubs:
You can extend the tree bloom season into summer by selecting the right blooming trees. Consider size, fruit characteristic, cultural requirements and flower color before making your selection. Select a tree that will not be too big for its location. Crowding a tree into a tight spot will often compromise the natural shape of the canopy and may put undue stress on the plant. Fruit is often forgotten during selection but should be seriously considered. Some trees will produce fruit that is attractive and makes a nice addition to the landscapes. Others may produce foul smelling fruit or attract unwanted birds or other pests. Most flowering trees will need at least a half a day of sunlight for good flowering. The number of blooms will often decrease with reduced light. Some examples of summer blooming trees include:
- Smoke Tree (Cotinus coggygria) – forms a multi-trunk tree and blooms in June-July with a light yellow hairy bloom that causes a smoke-like appearance.
- American Smoke Tree (Cotinus obovatus) – similar to above, except C. obovatus is a native and tolerant of drought conditions. Blooms white.
- Franklin Tree (Franklinia altahama) – a white blooming, native tree that must have full sun. Does best with irrigation and has a great red fall color.
- Seven-son Flower (Heptacodium miconiodes) – white flowers are followed by attractive fruit and reddish purple bracts that remain showy until frost. Multi-stemmed tree with papery bark.
- Crapemyrtle (Lagerstroemia indica) – hybrid cultivars of this multi-trunk tree allow for a great variation in bloom color and bark characteristics. Prolific summer bloomer.
- Sweet Bay Magnolia (Magnolia virginiana) – a native, white blooming magnolia that can be grown in poorly drained sites
- Mountain Stewartia (Stewartia ovata) – a native, white blooming native tree with exfoliating bark. Prefers moist soil and part shade.
Rhododendrons and azaleas will benefit from an application of fertilizer this time of the year. With these plants it is best to use fertilizers specially formulated for acid-loving plants. Fertilizers that supply nitrogen in ammonium form are preferred. A fertilizer analysis similar to 6-10-4 applied at 2 pounds per 100 square feet to the soil surface is usually adequate. Excessive applications can damage shallow roots. Fertilizer should not be applied after August 15 since emerging new growth will be killed by frost. Rhododendrons and azaleas need a pH of 5.5. Soil test to find your pH and use iron sulfate or agricultural sulfur applied to the surface to lower pH if needed.
Webbing at the ends of branches is evidence of the fall webworm. Several generations of this pest will occur in a summer. Prune out the webs that can be reached. If chemical control is to be used, it may be advantageous to spray nearby foliage with Bt (Dipel 2X, Biobit, Caterpillar Attack, Larvo-Bt and others) and thus conserve the natural enemy complex that helps regulate fall webworm populations.
Vegetables and Herbs:
Is Colorado potato beetle giving you fits this year? Control failures in home gardens with Sevin or Thiodan are commonplace. The recent release of M-Trak and other sprays with the naturally occurring bacteria Bacillus thuringiensis subsp. tenebrionis is effective and provides vegetable gardeners with a new weapon against these destructive insects. Bt should be applied just after egg hatch and every 5 7 days until harvest. After Colorado potato beetles ingest the bacteria, the larvae will stop feeding but may remain on the plant for several days before dying. Treat again if rain occurs within 24 hours after application. Another Bt product called Raven, which contains a specific strain EG7673 of Bt subsp. kurstaki., also works against Colorado potato beetle.
Squash vine borer moths are active now on squash, pumpkins and gourds. Late afternoon sprays of endosulfan (Thiodan) or carbaryl (Sevin) will control the larvae. Treat once a week for four weeks. A second generation of moths will emerge in August. Treatment may also be needed at that time if harvest is to continue into the late summer.
How do you know when it’s the right time to harvest herbs? Of course that answer will vary depending on which herb you are growing. Here are few of the more commonly grown herbs and their harvest information.
Basil (Ocimum basilicum) is a popular, tender, annual herb. It is grown for its aromatic leaves, which are used fresh or dried as a flavoring. Basil leaves are cut just prior to the appearance of flowers. Cut the foliage at least four to six leaves above the ground to allow for regrowth and a second crop.
Chives (Allium schoenoprasum) are a perennial herb used for making vinegars and is added to soups, salads, vegetable or fish dishes. To harvest chives, cut leaves 2 inches above the ground.
Dill (Anethum graveolens) is a hardy annual and commonly grown as a seasoning for soups, fish and pickles. Fresh leaves should be harvested before flowering begins. Harvest seeds as soon as seed heads are brown and dry. Dill is also great in butterfly gardens since it is a host plant for some larvae.
Mints (Mentha spp.) are aggressive growers and should be grown in containers to avoid hostile take-overs of gardens. The young, tender leaves and stems of Mint can be harvested as it comes up in the spring.
Thyme (Thymus vulgaris) is a small, perennial shrub. It is use often in French cuisine. Harvest the entire plant by cutting it back to 2 inches above ground in midsummer. A second harvest can be expected before the season ends.