August 25, 2015. Two-spotted Spider Mites in Hops

We received the following images of hops last week from Steve Jensen, Rustling Bines Hop Farm. I am including them in this entry with his permission. Although symptoms on the cones like these can be caused by several plant diseases, including Alternaria cone disorder, the primary problem with these leaves and cones is an infestation of two-spotted spider mite (TSSM).

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Chelsea Gordon, OSU Dept. of Entomology, confirmed the diagnosis and provided the following advice:

Infestation of cones with two-spotted spider mite (TSSM) leads to the cones being unusable to brewers. The mites decrease the quality of the cones, can cause shattering of cones during the drying process, and are themselves a contaminant. Any cones showing that type of browning are likely infested with mites and should not be sold to brewers. The effective miticides labeled for hops have relatively long pre-harvest intervals (PHIs) (most are 14-28 days). TSSM populations grow very quickly in hot and dry weather. This summer turned out to have the perfect conditions to cause TSSM headaches for many growers. Early in the summer rainy, cooler weather kept TSSM levels at lower, less detectable levels, then right when cones started to form it became hot and dry, leading to TSSM population explosions. The best thing to do when we have hot and dry conditions is to scout the hop yard thoroughly for mites. A good method for scouting is to walk your hop yard in a “W” pattern selecting leaves from 5-10 plants on each leg of the “W”, and being sure to pick leaves from various heights. The mites are found on the underside of the leaves and can be seen with a hand lens. More than two adult mites per leaf in June indicates that a miticide should be applied. By mid-July, that threshold increases to five to 10 mites per leaf. The main goal of controlling TSSM is to keep them out of the cones. As long as their populations stay low they will stay on the leaves.

Michigan State University rereleased a helpful article this year following their TSSM outbreaks:



August 25, 2015. More Pumpkin Downy Mildew in Southern Ohio

Downy mildew was confirmed on a pumpkin sample from Pike County, OH today. This is the second southern Ohio county with a recent downy mildew outbreak. Pumpkins and squash in southern and central Ohio need to be protected from downy mildew with fungicides. Downy mildew has been widespread in northern and central Ohio in cucumbers and melons much of the summer, but has not been reported yet in squash or pumpkins. Both crops should be scouted regularly for downy mildew symptoms in northern Ohio counties. There is evidence that many of the fungicides previously used for downy mildew management have become ineffective due to the development of insensitivity in the downy mildew pathogen. It is critical to include a protectant fungicide, e.g. chlorothalanil, in a tank mix with a downy mildew fungicide such as Ranman. Ranman must be alternated with a fungicide with a different mode of action, such as Zing!, which also contains chlorothalanil in a premix with zoxamide. Dr. Mohammad Babadoost of the University of Illinois has noticed that commercial pie pumpkins treated with Bravo Weather Stik (chlorothalanil) develop symptoms, but the pathogen does not sporulate well in the lesions, resulting in much slower spread than in non-sprayed pumpkins. We don’t know if the southern and central Ohio downy mildew pathogen “type” is the same as the Illinois type, and will respond in the same way, but if so growers may benefit from the use of chlorothalanil in a protectant program for pumpkin downy mildew.

Keep in mind that pumpkins also need to  be protected from powdery mildew.  Quintec and Torino are two of several effective fungicides to manage this disease.

August 19, 2015. Downy Mildew on Pumpkins

Downy mildew was found on pumpkins last week in Scioto County, OH.  There have also been reports of pumpkin downy mildew in Kentucky and Illinois.  Downy mildew was also reported in Clark County, OH on cucumbers. Downy mildew can be quite severe on pumpkin leaves, as shown below.  Look for the angular brown lesions on the leaves.  We found a great deal of the fuzzy look (sporulation) of the pathogen on the underside of these leaves.  Downy mildew is managed using fungicides such as Ranman plus Bravo, alternated with Zing or another downy mildew product; products should be applied weekly.


As the summer winds down and cooler weather, with heavy morning dews, becomes common, we can expect downy mildew to ramp up. Sporangia of the downy mildew pathogen move from plant to plant through the air. They do not survive well on sunny days, but can move for long distances under overcast skies. It is important to keep downy mildew to a minimum on all types of cucurbits – not only to protect yield, but to prevent spread of the disease to other fields – near and far.