White Rot Update
Crystal Stewart, Extension Vegetable Specialist
Eastern New York Commercial Horticulture
June 22, 2016
Earlier in June I sent a garlic sample to the diagnostic lab hoping that I was wrong. The sample was covered in small black sclerotia, the size of poppy seeds, and white fungal hyphae crept up the stem. The results, unfortunately, matched the field diagnosis: White Rot. Within a couple days additional calls came from up and down the Hudson Valley as well as one in Western NY with similar suspicions. These samples have also gone to the lab for verification, but it looks like the latest pest to move back into the state is this nasty fungus.
White Rot, Sclerotinia cepivorum, decimated the onion industry in New York in the 1930's before being eradicated through careful management. More recently, in 2003, it infected 10,000 acres of garlic in California, leading to the abandonment of some garlic fields and adoption of strict containment rules. White rot has been confirmed in Northeastern states over the last decade as well, with New York being one of the last to discover the disease.
The primary reason that White Rot is such a concern is because the sclerotia, or reproductive structures, can remain dormant in the soil for up to 40 years, attacking any allium crop planted into the soil under favorable conditions. This spring was ideal for infection due to the period of cool, moist weather we had. Optimal temperature for infection is 60-65 degrees F, but infection can occur anywhere from 50-75 degrees F.
Once garlic has white rot, it generally declines rapidly. Leaves will yellow and the plant will wilt, not unlike a severe fusarium infection. However, unlike with fusarium, white rot infected bulbs are covered in black sclerotia and white fungus. To add to the confusion, another disease CAN look similar. Botrytis also causes black sclerotia and white fungal growth. However, Botrytis sclerotia are quite large, often larger than a pencil eraser.
So, what do we do now? We're still working on long-term management strategies, but the most important steps to take now are vigilance when culling (look at the plants you are pulling for symptoms like you see in this article, and if they are present, call us to take a sample and have the disease verified) and, if you see anything suspicious, reduction of movement of inoculum. The main ways diseases get moved around are by dumping culls (compost, field edges, etc) and my moving soil on equipment. Throw away your culls, and wash equipment that may have come in contact with suspicious garlic or the soil it is growing in. Everything from cultivation equipment to harvest bins should be cleaned.
We will keep learning about this disease and will keep sending out information, particularly to help you make decisions about what to sell and buy. For now, remember that the west coast has learned to manage the disease, and we will too. -Crystal Stewart, ENYCHP
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