News

July 2010 What's Hot on the Hotline

07.19.10

What’s Hot on the Hotline

July 2010

Scaleinsectproblems continue to show up in the Plant Clinic. In the summer, scale is now noticed on euonymus, pine, and pittosporums. Most scale insects form a protective shell or waxy covering that doesn’t mix well with water; and what do we mix most pesticides with to spray? We use water. My preferred treatment for scale is to use horticultural oil 2-3 times at about 10 days. But the summer’s heat keeps me from making this recommendation. This lightweight oil has the potential to burn plant leaves in the heat. If we could use horticultural oil, it works by both suffocating insects and the oil helps pesticide absorption by the target pest.

So what is a gardener to do? One strategy is to monitor for “crawlers”. These are the vulnerable larva stage of the insect before it has a chance to form a hard shell.  This is a lot easier said than done; crawlers are usually very small and hard to see. Here is where a hand lenses or magnifying glass comes in handy. Depending on the scale, these insects can have one annual big hatch or several over the span of a season so identification of the specific scale is helpful.  But generally speaking, most insects time a hatching to coincide with warm weather in the spring. This way the next generation can move to part of the plant with adequate food supplies. So if plants have a history of scale, we can plan several treatments with horticultural oil in the late winter-early/spring. If gardeners are just discovering a scale infestation, I would recommend they make one treatment in the fall, after the heat has abated, with a mixture of horticultural oil and an insecticide like Malathion. They will receive the most benefit from a spring treatment next year.

Waxy Plant Hoppers: You may not recognize this pest but you probably have seen the waxy trail it leaves behind. The substance looks like someone took a cotton ball and rubbed it along a plant letting the cotton fibers trail down stems. The white waxy substance looks like a fungus to many gardeners. But these insects are only very minor pests of plants and treatment is usually not warranted. As I mentioned earlier, many gardeners think this is a fungus.  It isn’t so they don’t need to spray with a fungicide; it will not make the white cottony stuff go away any sooner.

Tomatoes - it’s almost not worth it. It is enough to make a gardener cry. The tomato disease presence this year has been very high. Well, if anyone has any tomatoes left in the garden, they likely are not setting fruit (because of the heat) and equally as likely are riddled with diseases. But July is not the time of year to think about what might have been, but to envision what may yet be. As tomatoes wane out, we need to start planting seeds for the fall vegetable garden. They will grow vegetatively fine in the summer’s heat. It’s hoped that they will start flowering about the same time that the nights cool down enough to make pollination likely. Now if the tomato gods smile on us, you’ll hopefully get a healthy crop of tasty tomatoes, but don’t be surprised if winter comes calling and your tomato plants have a lot of green tomatoes still on the vine. Pick what you can the night before the frost and find a good chutney recipe.

Sooty mold on crape myrtles and gardenias - Let’s start with a littlereview of sooty mold. Sooty mold is a common household mildew, which grows in a sugar water substrate called honeydew. Insects feeding on sap extracted from landscape plants produce honeydew. Not all of this sap is consumed by feeding insects. Some of the sap leaks out, covering plant leaves and finally, sooty mold starts growing. Most homeowners notice the black sooty mold in July and August.  Unfortunately, the cause of the problem, which is sucking insects like aphids, whiteflies or scales, are often gone. Scale insects will still cause damage, but aphids usually have long since left the scene of the crime. Remember, before we recommend treating for insects, make sure the pest is still present. Encourage homeowners to look under a leaf or two before they start to spray. A favorite control measure of mine, horticultural oil, will effectively kill insects and helps sooty mold slough off.  Keep in mind that oil must evaporate off leaf surfaces an hour before temperatures reach 88F.

Turf:Finally, summer has arrived. The cool spring, overcast weather, and moderate rain led to a lot of Large Patch this spring, especially in centipede and St. Augustine. The only good thing to say about the situation is that it is over. I never thought I would love to see 90 degree weather, but that is when the Large Patch stops. I am still seeing photos of spring damage in the Plant Clinic, but now, on to the usual summer problems. Chinch bugs do attack other turf, but they have a real preference for St. Augustine. The typical symptom is an apparent droughty area (browning or dried out look) in lawns even when adequate water has been supplied. Submerging a suspect sample in a bucket of water is a good way to detect the insect.  Take the samples from the margin of good and bad turf; also remember to submerge the sample for 5-15 minutes.

Mole crickets; the best time to treat for them is late June and early July. If mole crickets are suspected, have clients flush the suspect area with soapy water, 2 TBS per gallon. If mole crickets are found, then treat the area of damage or infestation, a foot or two into healthy looking turf. Generally, the entire yard does not need to be treated.  Here is an NC State website with some good information.

http://www.turffiles.ncsu.edu/Insects/Mole_Crickets.aspx.

I know I said the focus of this month would switch to insects, but there is always one disease out on the horizon. In July and August gray leaf spot starts showing up in St. Augustine turf. If this summer is as wet and as humid as usual, gray leaf spot has the potential to become a serious problem.  As the name implies, its most distinguishing characteristics are the ashen gray lesions on leaf blades.  Lesions usually have distinctive purple or black margins and eventually the lesions coalesce to kill the leaf blades. This disease can quickly damage large sections of turf and the patch mimics Large Patch in appearance.   This disease is aggravated by excessive growth and excessive leaf moisture. If noticed early, modifying cultural practices can effectively treat this problem. Water less because this fungus needs nearly ten hours of leaf moisture to germinate and infect new growth, or water very early in the morning. Extended periods of leaf dampness explain why the fungus is always worse under trees or in shady areas.  If you have St. Augustine grass, shady areas should be monitored for initial infection. The next cultural practice is to ease up on the fertilizer. This pathogen relishes soft new growth. Reducing the nitrogen can slow growth in the grass and slow the pathogen. Good sanitation is another quick, cheap fix.  Bag and dispose of lawn clippings from infected areas.  Chemical controls include Mancozeb, Banner Maxx and Bayleton. The combination of cultural practices and fungicides should keep this disease under control.

Upcoming Events

July 20th, from 9:00am –till noon, “Start a Fantastic Fall Garden”.  Is the heat and frustration of vegetable gardening got you cursing the tomato gods? Well, in about a month, gardening will become a little easier. In fact, fall/winter gardens can be a more rewarding vegetable experience than the traditional spring/summer garden. But like everything in life, to be successful requires a little planning.

Prepared by:

Ken Wells, New Hanover County Consumer Horticulture Agent