Thursday, August 22, 2013
With all the rain we have had the Indian Hawthorn, Raphs or Raphiolepis have been really suffering. Raphs have been plagued with leaf spot for years; however, this wet year has taken its toll on them. It seems like right after the Red Tips (Photinia) were virtually wiped out by Entomosporium leaf spot, the diseased began attacking the Indian Hawthorn. Indian Hawthorn and Red Tips are in the same plant family as roses (Rosaceae).
When dealing with a plant that is very susceptible to a leaf spot disease I like to think of several different factors:
1. Is this plant worth keeping in the landscape or should I replace it with another plant that is not susceptible to disease.
2. Is this plant worth spraying every 14 – 28 days to keep it in my landscape? To keep an Indian Hawthorn alive, it needs a life-support system. The plant must be sprayed at least monthly or it will get leaf spot again.
3. What cultural practices can I do to help relieve the pressure of the disease? The removal of fallen foliage (sanitation) is key when dealing with a leaf spot disease. Having a healthy soil, as determined by a soil test, is also very important because a stressed plant is more susceptible to disease. Providing the correct amount of water preferably through a drip system, so the plants are not over-watered or drought stressed. Proper fertility as determined by the soil test is also important. Use nitrogen fertilizer very sparingly in small amounts because flushes of new growth are more susceptible to leaf spot. Choose “resistant” varieties such as “Olivia.” This does not mean that this plant will never get this disease; it is just more resistant to the disease. Mulch like Cotton Burr Compost will help prevent splashes of water drops that could spread the disease. Also this mulch will lower the watering needs of the plants. Bioscience products like KeyPlex should be considered. KeyPlex will thicken the cuticle of the leaf making more resistant to the disease as well as more drought resistant. Pruning for good air movement.
4. What control products will work best on this disease? If you decide to spray, be prepared to spray often. Honor Guard, Banner, Dithane (Mancozeb) and Kocide are good choices. These products should be used in rotation and according to label. I like the lime-sulfur idea or lime-copper spray for the reason that the original Lamson–Scribner invented this product in an effort to save the French wine crop in the late 1800’s. He called it Bordeaux mix (unfortunately Bordeaux mix is not available anymore). When spraying these chemicals, an appropriate surfactant should be used. Certain surfactants work better than others with particular products.
I’m in yards all the time and this disease is the most common disease I see in our Lowcountry landscape. I usually recommend replanting the area. I can understand spraying roses all the time. Indian Hawthorn – ah, not so much.
It is time to get your preemergent products out before your winter annual weeds start to germinate. With all the rain, Annual Bluegrass (aka Poa, Poa Annua, that pain in the “grass” grassy weed with the white seed head) should germinate early and often.
Prevention, being pro-active, and protection is the best way to deal with winter weeds.
Always read, understand and follow product label. The product label is a federal law.
Bill Lamson-Scribner can be reached during the week at Possum’s Landscape and Pest Control Supply. Possum’s has three locations including one at 481 Long Point Rd. Bring your questions to a Possum’s location, or visit us at http://www.possumsupply.com. You can also call in your questions to “ The Garden Clinic,” Saturdays from noon to 1 p.m. on 1250 WTMA. The Horticulture Hotline is available 24 / 7 at possumsupply.com.