Summer Solstice Welcomes Brown Patch

June is in full swing and so is brown patch in tall fescue lawns and landscapes.  Brown patch, caused by the fungus Rhizoctonia solani, is the most common disease in tall fescue during late spring and throughout the summer months in North Carolina.  Brown patch infections can start as early as April in some years with full blown outbreaks occurring by late May and early June in most years.  As the name implies, symptoms are brown to tan areas of turf that are roughly circular patches that range from a few inches to several feet in diameter.

Brown Patch Lesion on Tall Fescue Leaf

The two most common mistakes managers of tall fescue make are fertilizing too late or too much in late spring and over watering.  Tall fescue should not be fertilized after the first of May, unless you are using ultra low rates (< 0.25 lb N/M) with iron for a color effect.  The recommended amount of nitrogen on tall fescue per year is 3-4 pounds per 1,000 square feet.  Most people will apply a pound or two in the fall and a pound or two in the spring.  When in doubt, submit a soil test to ensure you're feeding your lawn the right nutrients at the correct amounts.

Watering should be done only as needed to prevent drought stress.  When you do apply irrigation, do it deep and infrequent instead of watering every day.  It is a common mistake for homeowners to set their irrigation system on a schedule and forget about it.  Remember, fungi love water and if you over water, you're giving the advantage to the fungi, not the turfgrass.  The ideal time to water your lawn is in the early morning hours before sunrise.  Irrigating during late afternoon or early evening is the worst thing you can do because this extends the leaf wetness period, however brown patch will love you for it!

Symptoms of Brown Patch in Tall Fescue

Need help knowing when and how much to water your lawn?  Try out our online water management tool at the following link: http://turf-ims.ncsu.edu/

For more information about brown patch, including control recommendations, please visit the following link: http://www.turffiles.ncsu.edu/Diseases/Brown_Patch.aspx

Be sure to check out other posts from NC State Turf Pathology here

Thanks to Lee Butler, Turfgrass Diagnostician, for providing this post.

Phytophthora Crown Rot of Squash

Last week we received a yellow squash sample from a commercial field operation in the foothills of North Carolina. As soon as we ripped open the package and the smell hit our noses, we knew we would find something rotten inside! Expecting the worst, we dug in to diagnose the sample. Luckily, the symptoms were classic for Phytophthora crown rot and easily diagnosed by plating out infected tissue on semi-selective media.

Crown Rot (Photo: E. Lookabaugh)

Phytophthora crown rot, also known as Phytophthora blight, is one the most destructive diseases of vegetables in North Carolina. The crown rot pathogen, Phytophthora capsici, attacks peppers, tomatoes, eggplant, squash, pumpkin, cucumbers, watermelons, and muskmelons. Symptoms vary depending on the crop and the part of the plant affected. On squash and pumpkins, a watery crown and fruit rot are common symptoms. Wilting and death soon follow. Fruit that comes in contact with contaminated soil develop dark lesions with concentric rings.

Fruit Symptoms (Photo: NCSU Plant Pathology)

Phytophthora is a soilborne water mold that produces swimming spores, called zoospores. Because the zoospores swim through soil water or are splashed onto susceptible tissue, Phytophthora crown rot is favored by heavy rainfall or irrigation. Excess water accumulates in the crown of squash and pumpkins, making these two hosts particularly vulnerable to crown infection.

Crown Rot (Photo: E. Lookabaugh)

Controlling crown rot can be difficult because the pathogen survives in soil for many years. Alternative crops for infested fields include tobacco, potatoes, and sweetpotatoes, which are not susceptible to Phytophthora capsici. Rotating with corn and small grains for 2 to 4 years is highly recommended. Crucifers like cabbage or broccoli also are good rotation crops. Avoid planting in poorly drained or low areas, and avoid excess irrigation. Some peppers cultivars have good to moderate crown rot resistance. Farms with a history of Phytophthora blight may benefit from the use of chemical sprays.

For more information, see our fact sheet.

Pest Alert: Impatiens Downy Mildew

Impatiens downy mildew detected in multiple landscape locations in North Carolina 

Kelly Ivors, NC State University 

Downy mildew of impatiens is caused by the ‘fungus-like’ organism Plasmopara obducens. The group of organisms that cause downy mildew diseases are not true fungi- they are more closely related to the well-known plant pathogens Phytophthora and Pythium than they are to true fungi. This is an important distinction to understand because many of the traditional fungicides used to control fungal diseases of plants do not have efficacy against the downy mildews. All types of propagated Impatiens walleriana, including double impatiens and mini-impatiens, and any I. walleriana interspecific hybrids, such as Fusion® impatiens, are susceptible to downy mildew; however, all New Guinea impatiens (I. hawkeri) and interspecific hybrids such as SunPatiens® are tolerant to downy mildew. No other bedding plants are known hosts of this particular downy mildew, although there are a few other downy mildew species that attack other floriculture plants like coleus and basil. 

What does downy mildew look like? 

A really good resource about identifying the disease, as well as disease control information, can be found here. 

In addition, a webinar presented by Dr. Colleen Warfield of Ball Horticultural Inc. can be found here. 

Downy Mildew (Photo by: Kelly Ivors)

Downy Mildew (Photo by Kelly Ivors)

Downy mildew likes cool, wet/humid environmental conditions. The current conditions we’ve experienced recently across the state of North Carolina are conducive for this disease. The important thing to remember is that downy mildew is spread by wind currents, water splash or by the movement of infected plants. We know that the disease is now in our area and that the spores of the pathogen have the ability to spread long distances in air currents. Be on the look-out for it! So far it has been confirmed in both the western and piedmont areas of North Carolina. 

Fungicide treatments are not recommended for plants in the landscape; instead, all infected impatiens should be pulled from the landscape and destroyed. Fungicides are not always 100% effective at eliminating the disease. Allowing infected plants to remain in the landscape may allow the pathogen to overwinter as resting structures (called oospores), which can start a new epidemic later in the year or in following years if impatiens are replanted in the area. New Guinea impatiens, coleus, begonia, or other available bedding plants are safe to reset in the affected area.