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With more spring-like weather gracing the state at the end of April, potato planting has started in the southern part of Central Wisconsin. Spud growers in northern Central Wisconsin will start the beginning of May.

Warm soil temperature are expected to provide quick emergence, according to the UW-Extension Vegetable Crop Update. All the snow dumped on the state in April provided good soil moisture for seed germination. 

Here are a few highlights from April updates.

Downy mildew on hops

Hop shoots are just beginning to emerge in southern parts of Wisconsin, so it is important to be aware of the first signs of downy mildew as temperatures become warmer and hop growth increases. 

While April showers bring May flowers, it also brings downy mildew, with spikes typically seen after cool, rainy weather. Common symptoms of downy mildew infected spikes include stunted, brittle shoots, often showing yellow-green/chlorotic coloration. Leaves are typically seen to be curling downward, particularly leaves closer to the ground. Black/gray fuzz of sporulation may be visible on the undersides of leaves. 

Early disease management should focus on reducing the initial pathogen inoculum as much as possible to prevent further plant infection later in the season. Due to the aggressive and potentially devastating nature of this disease in our Wisconsin climate, chemical intervention is often prescribed, according to the crop update.

A popular active ingredient to use at this time of year (post-prune but before training) is mefenoxam, which has good systemic activity within the hop plant and has been demonstrated to be highly effective. A complete list of fungicides registered in Wisconsin for hop downy mildew control can be found under the “Hops” tab of the UW Vegetable Pathology website.

National Late Blight 

USAblight, a national information portal on late blight, is up and running for this year in an effort to support the detection and characterization of late blight on tomato and potato crops. 

Late blight has been confirmed on potato and tomato in Florida, according to the UW-Extension crop update. All case reported have been the predominant genotype found in Wisconsin in recent years, which can generally be managed with the use of phenylamide fungicides such as mefenoxam and metalaxyl.

 However, the UW-Extension lab received a potato sample from northeastern Florida with a genotype that cannot be managed with phenylamide fungicides, which poses some concern for management. 

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Problematic weed herbicide

The Wisconsin DATCP has approved Syngenta's request for a new Section 24c Special Local Need Label for Dual Magnum herbicide to assist in management of problematic weeds such as the nightshades. This label is valid in Wisconsin only and through December 31, 2022.

The label includes a long list of minor vegetable crops where weed management options are extremely limited. Dual Magnum herbicide controls several annual grass and broadleaf weeds prior to their emergence. It will not control any weeds that have already emerged. 

In general, the risk for crop injury increases when the herbicide is applied during or around cool, wet weather, according to the vegetable crop update. The use rate varies primarily by crop and soil type. Details are contained in the label that can be found on the DATCP special pesticide registrations web site: datcp.wi.gov/Documents/SpecialUses.pdf.

The 2018 Commercial Vegetable Production in Wisconsin Guide is available for free download at learningstore.uwex.edu/assets/pdfs/A3422.PDF or can for $10 from the UWEX Learning Store. 

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