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Showing posts from August, 2019

Sightings from the field: week of August 26-30, 2019

Author: Natalie Hoidal, UMN Extension horticulture educator
Alternaria (black / brown leaf spot) in Cole crops - Rice and Chisago counties
We've seen Alternaria leaf spot showing up on cole crops on a few different farms this week. Alternaria leaf spot is caused by three different strains of the Alternaria fungus: Alternaria brassicicola, A. brassicae, and A. raphani. It can be identified by the target-like appearance of spots on the leaves, forming concentric rings. Leaf spots tend to appear first on the lower leaves, and will often break open and fall out. If you're seeing Alternaria for the first time in your fields, the disease likely came on infected seed. 

More information on Alternaria.
For conventional growers, the Midwest Vegetable Production Guide contains a list of effective fungicides. For organic growers, options are limited, with organic fungicide products showing limited success. Practicing good sanitation is key. For next year's planning, make sure to rotate …

Consider planting a cover crop this fall

Author: Vivian Wauters, PhD student, Applied Plant Sciences - Agroecology

As the daily high temperatures slowly drift downward, and fall vegetable crops start to appear at the farmers markets, there might be some open space on your farm that won’t be planted to vegetables until next year. If so, one option could be to try out fall-seeded cover crops!

Why fall-seeded cover crops?

Cover crops can contribute to soil organic matter, suppress weeds, add N (legumes only), protect soil from erosion, and soak up excess nutrients in the soil, preventing leaching, among others. In some Minnesota vegetable rotations, there are fields that are finished before the first frosts (e.g. peppers or summer squash), and without planting anything else, they would lie bare during the whole winter. The bare soil would be vulnerable to erosion and nutrient leaching, but by planting a cover crop, you can protect the soil and the nutrients in it, and maybe even get a head start on soil fertility for the next se…

Limited fruit set and fruit abortion in winter squash and pumpkins

Author: Natalie Hoidal, UMN Extension horticulture educator

We're seeing some cases of low fruit set and / or fruit abortion in pumpkins and winter squash. If this is happening on your farm, there are a couple of potential explanations:

1. Pollination
Pumpkins and squash are dependent upon insect pollination. Male flowers bloom about a week before female flowers, and flowers only bloom for a few hours in the morning, so it's crucial that conditions are right for pollination. Penn State Extension has an excellent, in-depth article on pollinators in pumpkins and squash. Some of the highlights include:  Bumblebees and squash bees (Peponapis pruinosa) are the best pollinators of pumpkins since they forage in the morning, and because squash bees have a lifecyle that's perfectly timed with the lifecycles of cucurbits. Cucurbits include pumpkin, squash, melons, cucumbers, and zucchini. Creating habitat on your farm for nesting sites may help boost pollination on your farm. For bumb…

Garlic Bloat Nematode update

Garlic Bloat Nematode - make sure to purchase seed that's been tested The plant disease clinic has confirmed the presence of Garlic Bloat Nematode (Ditylenchus dipsaci) from three separate farms this year, one of which had it last year as well. This is not unexpected or different from a typical year, but it's a good reminder to only buy seed from vendors who have tested negative for the nematode. Garlic Bloat Nematode is spread predominantly through seed, and once present on your farm is exceedingly difficult to get rid of. If you purchased garlic seed from the Sustainable Farming Association's Garlic Festival, all seed at the festival was screened and confirmed to be nematode free. For more information on the nematode, continue reading here.

Are you still looking for garlic seed?  Our friends at SFA maintain a list of growers who have seed available:

Upcoming workshop and educational materials For those just start…

Spotted-wing Drosophila (SWD) Concerns for Wine Grapes, Near Harvest

Authors: Bill Hutchison, Eric Burkness, Dominique Ebbenga & Matt Clark, MN Extension IPM Program, Dept. of Entomology, Dept. of Horticultural Science, University of Minnesota, St. Paul campus
Fig. 1. Spotted wing drosophila male (left), with characteristic spots on the wings, and female (right), with serrated ovipositor (egg-lay device). Photo: Sheila Fitzpatrick, Agriculture & Agri-Food Canada, Pacific Agri-Food Research Center, Agassiz.

Spotted-wing Drosophila (SWD) trap catches continued to remain high at our four remaining locations this week. In addition to fall raspberry risk of damage, a key concern for grape growersshould be the high numbers of SWD at Chanhassen (Hort. Research Center, HRC), and at Hastings. Traps in our network are effective at catching both male and female flies (Fig. 1). As we approach wine grape harvest in the next 2-3 weeks, growers should remain vigilant in monitoring SWD (ideally, using traps located at on-farm vineyards), and if flies are presen…

Keep an eye out for Brown Marmorated Stinkbug

Authors: Bob Koch (Extension soybean entomologist), Rafael Aita (Graduate student) and Natalie Hoidal (Extension educator - vegetable production systems)

The Brown Marmorated Stink Bug (BMSB), Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) is a relatively new invasive insect in Minnesota with a wide range of host crops, including many fruit and vegetable crops. It was first detected in the U.S. in the mid-1990’s and in Minnesota in 2010. Entomologists expect that as populations build, the BMSB may become an important pest species.

In its native region of China, South Korea, Japan, and Taiwan, it is a significant pest of fruit trees. In the US, it feeds on wine grapes, apple trees and other fruit trees, various beans species (soybean, green bean, dry beans), raspberries, grapes, tomatoes, peppers, sweet corn, and various ornamental plants. It feeds by inserting needle-like mouthparts (stylets) into developing fruit, which can cause abortion of seeds, deformation, and discoloration…

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…

Corn Earworm Alert for Minnesota Sweet Corn, Tomatoes, and Green Beans

Bill Hutchison, Eric Burkness & Suzanne Wold-Burkness
Minnesota Extension IPM Program, Dept. of Entomology, UMN, St. Paul campus

This past week, our trapping network detected the first significant increase in corn earworm (CEW), Helicoverpa zea, moth flights at for two locations: Blue Earth (MN/IA border), and Owatonna. 
In previous years, Blue Earth is often the first location to experience the first increase in moth flights, and this year’s catch is right on schedule for early August. Moth flight numbers averaged over 12 per night at Blue Earth (as of 8/13), and over 5 per night at Owatonna.  Our action threshold to initiate sprays for CEW in sweet corn is when trap catches average more than 5 moths per trap per night for 2 consecutive nights, and sweet corn is between 15 to 50% silk (for the first spray).  
Subsequent sprays should be based on continued moth flight activity with sprays applied approximately every 5-7 days prior to harvest (see below). As noted previously, CEW i…

SWD Flights Continue to be Active in all Late-season Berry Crops

Authors: Bill Hutchison, Eric Burkness, Chulwoo Kim, Brianna Pomonis, Anh Tran, Dominique Ebbenga & Suzanne Wold-Burkness
MN Extension IPM Program, Dept. of Entomology, University of Minnesota, St. Paul campus

Spotted-wing Drosophila (SWD) trap catches continue to remain very high in all on-farm and research locations monitored. Traps in our network are effective at catching both male and female flies (Fig. 1).   Growers should remain diligent in alternating insecticides as much as possible (e.g., Delegate or Entrust [organic-certified], Mustang Maxx, and Malathion), and follow the pre-harvest and re-entry intervals, noted on the label for each insecticide. The most significant increase was Hastings this week, where wine grapes are now at véraison, with approx. 60% green berries. We will have more information next week regarding SWD management strategies for wine grapes. SWD numbers usually increase in wine grapes from late-August to mid-September, through harvest.

Spotted Wing Drosophila (SWD) Flights Remain High in Berry Crops & Nearby Forest Edge Borders

Authors: Bill Hutchison, Eric Burkness, Anh Tran, Dominique Ebbenga & Suzanne Wold-Burkness
MN Extension IPM Program, Dept. of Entomology, University of Minnesota, St. Paul campus

Spotted-wing Drosophila (SWD) trap catches continue to remain very high in all on-farm and research locations monitored, especially the past 2 weeks. Traps in our network are effective at catching both male and female flies (Fig. 1).  See Table 1 below for details. Growers should remain diligent in alternating insecticide products as much as possible (e.g. Delegate or Entrust (organic-certified) and Mustang Maxx, and malathion if needed), and follow the pre-harvest intervals noted on the label for each product.

An additional reason for the concern with high SWD numbers in traps is not only for the SWD catch within berry crops, but also the concern with the SWD “reservoir” confirmed again this summer in nearby forested areas or “tree lines” that often occur near berry fields.

Our previous sampling has show…

Silver Leaf Disease of Apple Trees Spotted in Minnesota Orchards

Author: Annie Klodd, Extension Educator - Fruit and Vegetable Production

Several apple growers have reported increased incidence of "silver leaf" on their trees this season. One question asked around this topic is whether the cold winter could have contributed to silver leaf. Before answering that question, let's talk a bit about what silver leaf is and how it spreads:

Silver leaf is a fungal disease of apple trees and many other deciduous trees that makes the leaves appear "silver" or gray. This is caused by a fungus called Chondrostereum purpureum. In addition to infecting leaves, it also forms conks (fruiting structures) on the trunks and branches of trees.
How Silver Leaf Spreads During wet conditions in the spring and fall, the conks release spores that can then infect wounds on the trees, like pruning cuts, splits from winter injury, or broken branches from heavy snow.

The fungus then resides in the xylem of the branches, and a toxin from the fungus moves…

Sightings from the field: Week of July 29th

We're adding a new column to the newsletter called "Sightings from the field". Since our team does regular farm visits, we see a lot of diseases, insects, and nutrient issues, but also a lot of cool and exciting things! By sharing what we're seeing on farms around the state, we hope that you'll appreciate an inside look at what other farmers are dealing with, and the creative approaches they're taking.

This week: July 29th. Natalie and Annie were up on the iron range visiting farms, so many of our photos this week come from the far north.

Chimera, Aitkin County

This one had us stumped at first. The grower had a row of peppers in the field, and about half of them were showing this streaking pattern on both the leaves and the fruit. We considered herbicide drift (not likely given the situation), a nutrient deficiency, or maybe even "burn" from an over application of fertilizer.

It turns out the streaking was caused by chimera, a genetic mutation that c…

What's Killing My Kale Episode 25: Integrating flowering plants and vegetable production

Author: Natalie Hoidal. Interviewees: Julie Weisenhorn and Nathan Hecht

In episode 25 of What's Killing My Kale, Natalie talked with Extension Educator Julie Weisenhorn, and recently graduated horticulture master's student Nathan Hecht. Both Julie and Nathan have been studying how flowering plants near fruit and vegetable plots impact pollination and fruit set. While we generally know that adding flowering plants to the landscape is good for pollinators and beneficial insects, we wanted to dig deeper and learn how much of an impact flowering plants can have, how to go about selecting the proper plants, and how the broader landscape impacts results. This is a longer episode, but it's packed with insight and good discussion. 

You can listen to and download the episode here.What's Killing my Kale is also available on iTunes. If you enjoy listening to our podcast, please leave a review on iTunes. As always, reach out and let us know if there are any topics you'd like us …