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Sightings from the field: August 5-16

Authors: Annie Klodd and Natalie Hoidal, Extension Educators for Fruit and Vegetable Production

In the last week, Annie visited berry farms in Quebec that are growing raspberries, strawberries, and blueberries under protected culture like high tunnels and exclusion netting. Natalie visited multiple farms around the metro area. 

What we did not see: Late blight! 

We had a false alarm this week - someone sent us a photo that looked eerily like late blight, but the UMN Plant Disease Clinic confirmed that it was not late blight. Phew! We checked in with our potato growing colleagues who run the NDSU / UMN Potato Late Blight spore trapping network, and as of last week, no late blight spores or DNA have been identified in filters, and no reports have been made. 

Tomato problems: the common culprits, Ramsey County

Septoria, bacterial spot, early blight, blossom end rot - these are all common problems at this point in the summer. In this case, we found all four (three diseases + blossom end rot, a physiological condition) occurring on the same plants.

Tomato plants exhibiting symptoms of Septoria, bacterial spot, early blight, and blossom end rot, August 9, 2019. Photo: Natalie Hoidal

Diseases: Continue to practice good sanitation, and send your plants to the Plant Disease Clinic to confirm which diseases are present. If you're planning to spray, consult the Midwest Vegetable Production Guide for up-to-date recommendations on products and rates. For organic growers, your options are limited to copper products for most diseases. If you're using copper products, make sure to spray in dry conditions - spraying copper in wet conditions can cause damage to your crops.

Blossom end rot: Blossom end rot is caused by insufficient calcium in the fruit of tomato and pepper plants. The cause is typically not actually a lack of calcium in the soil, but rather a failure to take it up. Getting a soil test is always important to make sure you've got enough nutrients and organic matter in your soil. However, blossom end rot is more often caused by too much, too little, or sporadic moisture. Tomato plants need consistent moisture throughout the season, so working to prevent both flooding and drought is critical for quality fruit set. If you're experiencing blossom end rot this year, consider flood prevention measures such as growing under plastic or using raised beds next year. Additionally, use irrigation during dry periods to ensure a consistent supply of moisture to your plants. More info on blossom end rot. 

 Exclusion net for spotted wing drosophila (SWD) control in blueberries

A farmer in Quebec tours a group of fruit Extension educators and researchers around his blueberry exclusion netting structure on Aug. 8, 2019. Photo: Annie Klodd.
In Quebec, one of the farms we toured has 0.8 acres of blueberries under a full canopy of exclusion netting. This is a new method being tested across North America for control of SWD, to minimize or eliminate the need for chemical control. According to the farmer, it also increases his yield by 20-25%, and increases berry quality by excluding weather and bird effects.

The 70 gram netting is draped on top of large posts scattered throughout the structure, held up by wires, and secured along the bottom on all four sides so as to completely exclude SWD. Bumble bees (2 boxes per acre) are brought it for pollination for a two-week period. The netting lasts around 10 years before replacement. However, the pieces are connected by zippers, so that if one piece is damaged, it can be switched out without needing to replace the entire net. For more details, attend the MOSES field day next week at Blue Fruit Farm, where Annie will describe this system and demonstrate exclusion netting.

Phytophthora in peppers, Dakota County

Phytophthora blight in peppers. Image: Howard F. Schwartz, Colorado State University, 

Phytophthora is a tricky disease to manage because it affects plants from multiple families. Susceptible crops include peppers and cucurbits (squash, zucchini, pepper, pumpkin). Phytophthora is a water mold, which means it develops a swimming spore that can travel through saturated soils. This is especially problematic during excessive rains and flooding, when water moves quickly across the landscape. Infected plants will quickly wilt and die. If the infection is limited to a couple of plants in the field, quickly remove the plants to help prevent the disease from spreading. See the Midwest Vegetable Production Guide for fungicide recommendations. Long-term, consider landscape modifications to prevent the movement of water between fields such as berms and perennial strips.

Long cane raspberries under high tunnels

Touring a farm growing long cane raspberries under high tunnels in Quebec. Photo: Annie Klodd.
In Quebec, several farms are starting to grow large quantities of raspberries under high tunnels. Rather than planting them in the ground, the plants are grown in pots and moved out of the high tunnel each winter. They then spend the next season outdoors developing primocanes while another batch of plants is moved into the high tunnel for floricane fruit production. This is a high input, high intensity system that requires a lot of labor. However, the innovative growers working on it feel that the added yield, quality, and market value of the berries makes up for the added management costs. Now, researchers on the tour are considering applying for grant funding to see how this system might be adapted for smaller scale farms in the Midwest and Northeast.
Large raspberries are ready to be harvested in a high tunnel in Quebec, Canada on Aug. 7, 2019. Photo: Annie Klodd.

Lower and lean method for trellising, Goodhue County

We've seen some very creative solutions for trellising indeterminant tomatoes in high tunnels over the course of the season. One method that works well is the lower and lean method. Plants are clipped to hanging strings for support, and as the plants reach the purlins (trellising support structure across the top of the high tunnel), the string on each clip is extended and the clips are moved horizontally along the purlins so that the plants are tilted. This allows the plants to keep climbing while keeping the fruit and a manageable height for harvest. 

Tomatoes trellised with a lower and lean system in Goodhue County, August 7, 2019. Photo: Natalie Hoidal

For more information on how this method works, check out this informational video about the method.

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