Monday, June 19, 2017

Biting, Stinging Insects and Gray Leaf Spot

Horticulture Hotline 06/19/17

Wasp, biting flies, flies, and mosquitoes – Tis the season. The summer started out with three wasp nests on my front porch. One was right by the door and two others were staring straight at you as you exited the front door towards the street. A few days later, I’m letting Ol’Boy, my pound hound, out of the back door, and there was a wasp nest right next to the door at eye level. Whitmire’s Professional Strength Wasp Freeze handles the situation once again. Wasp 0 me 2.

I felt like I was winning, until I went to my Mother’s house to cook up some vittles on the grill. I turned on the gas (the gas must have aggravated the wasp), then lifted the lid to light it. The wasp came pouring out of the grill and bit me six times before I even knew what was going on. Wasp win this battle.

Hopefully with the professional pest control managers and the readers of the Horticulture Hotline help, the war will be won by the humans, and only a few battles lost to the wasps.

The rains and high tides have the mosquitoes out in full force. Protect yourself!  

Between pop up thunderstorms, people going on vacation, and people just not mowing enough, gray leaf spot has exploded on St. Augustine grass.

Gray leaf spot (Pyricularia grisea) goes with St. Augustine like grits go with shrimp! Or like chinch bugs go with St. Augustine! To battle gray leaf spot, you are best employing many cultural practices and using limited control products if necessary.

Gray leaf spot looks like someone burned or dripped acid on the leaves of the plant.  There are little oblong spots on the leaf.  Eventually, these spots grow together and the leaf blade dies.  Whole areas of your grass can disappear at once when these leaf blades die.

Culturally there are several things to do to minimize your problem with gray leaf spot.  This disease likes high humidity and excessive nitrogen fertilizer.  To help alleviate the high humidity, mow your grass to a level that seems abnormal to St. Augustine.  Try to get it down to 2 ½ - 3 inches depending on the variety of St. Augustine grass.  Also try to mow every 3 – 5 days with a bagger.  This mowing will help get sunlight down to the crown of the plant, drying the leaf blades as quickly as possible.

Mowing is always hard to get someone to modify the frequency of cuts. “The landscaper only comes every 7 or 14 days” or “I mow every Saturday morning”, is what I usually hear. If you don’t want to cut it yourself in between visits by the landscaper (saving a trip to the gym and I have been told a cold beer is extra good after mowing), maybe you could hire a neighborhood kid or your kid to just mow the grass. No edging, blowing or weeding, just a quick mow.

Another alternative to you mowing is applying a growth regulator to your turf. These products work great at slowing your turf’s growth rate. Growth regulators are used extensively on golf courses and athletic fields. Growth regulators do a great job of managing your turf’s growth rate on your home lawn as well.

Consider trimming trees or shrubs to increase air movement through your yard.

This fungus like most fungi likes hot humid weather.  Minimize the amount you water as much as possible.  Wait until your lawn is getting a blue/green color and your foot prints stay in the lawn after you walk across it before you water. Unfortunately, you can not control rainfall as easily. In the Lowcountry, afternoon thunderstorms are a way of life, so keep the grass mowed as low as you can so it will dry out quickly. 

Hold off of the nitrogen fertilizer until you can get this disease under control.  If you need some color, you could add a product like Possum’s Minors to give you some green without all the nitrogen. Watch starving your grass because a malnourished yard is more susceptible to disease. Very low rates of an organic fertilizer or cotton burr compost might help it recover.

At Possum’s, I know we have had several customers that swear they control this disease by using our wetting agent with biostimulants, cotton burr compost, and / or SeaHume along with the above cultural practices. 

If you have to resort to a control product, make sure the product is labeled for Pyricularia grisea.  There are many leaf spot diseases on labels of control products but only certain products work on gray leaf spot on St. Augustine. We had one customer come in that had been applying a product that controlled Drechslera spp. and Biopolaris spp. leaf spot; however, the product was not labeled for Pyricularia grisea (watch where you shop). 

Honor Guard and Heritage are systemic products that you spray. Since this is a leaf spot fungus, the sprays seem to give good coverage over the leaf blade.  If you would rather use a granular product, Prophesy (same active as Honor Guard and Banner), or Fame are granular systemic products that are absorbed through the roots and will do a good job for you.