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CONTENTS

140 ..................................................................CORN STALK ROTS AND EAR ROTS

143 ..................................................................WISCONSIN FRUIT NEWS ISSUE 14

144 ..................................................................2020 IPM FIELD SCOUT TRAINING CLASS

144 ..................................................................PLANT DISEASE DIAGNOSTIC CLINIC (PDDC) UPDATE

144 ..................................................................SOYBEAN MIDGE UPDATE

CORN STALK ROTS AND EAR ROTSDAMON L. SMITH, ASSOCIATE PROFESSOR AND EXTENSION FIELD CROPS PATHOLOGY SPECIALIST, UNIVERSITY OF WISCONSIN-MADISON

The 2019 growing season is the third year in a row where we are going to end with many challenges for Wisconsin farmers. The excessively wet weather is challenging the last of corn silage harvest, and grain harvest has barely started in much of the state. Couple this with wet weather, delayed planting, and plant stress most of the season and there is a double whammy of stalk rot and ear rot issues to contend with this fall.

What is the Primary Stalk Rot Issue in Wisconsin?

Anthracnose stalk rot (Fig. 1) has been readily apparent for Wisconsin corn growers this season. Anthracnose stalk rot is typically worse in fields in a corn-on-corn rotation, and/or no-tilled, and planted to a susceptible hybrid. Reports and observations of lodging are starting to come in. In addition, to anthracnose stalk rot, we are also seeing Gibberella stalk rot picking up . This stalk rot seems to be showing up in late-planted corn-situations and especially wet fields. This isn’t surprising given the weather conditions and level of plant stresses from compaction, slow accumulation of growing degree day units, and foliar pathogens. Impending frost in much of the state this weekend will also end the growing season, meaning that plants already damaged by stalk rot will shut down. The clock starts ticking on what can be done and lodging becomes a considerable concern.

Frosted corn for silage will begin drying at a faster and constant rate, regardless of kernel or plant maturity. The primary aim for frosted corn meant for the silo becomes achieving an ideal moisture content for ensiling. With whole-plant corn silage, the ideal moisture range is 63 to 68% however with frost damaged or killed corn, achieving this dry matter for the entire crop may prove impossible. Actively monitor moisture during harvest and segregate the crop if moisture dips below 55%, to avoid silage storage and stability issues later on.

What should I do if I have a field with stalk rot?

In fields were stalk rot’s an issue, HARVEST AS EARLY AS POSSIBLE to avoid yield losses from lodging. Silage corn fields should also be chopped as soon as possible, monitoring moisture and being

UNIVERSITY OF WISCONSIN CROP MANAGER OCTOBER 17, 2019

Figure 1. Anthracnose stalk rot of corn.

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sure to take extra care in packing the bunker. Delaying harvest for grain corn will increase the likelihood of lodging which will increase harvesting issues. Once conditions dry enough to allow combines to run, fields with higher levels of stalk rot and/or lodging should be prioritized for harvest.

What should I do about stalk rot for next season?

Management of of any of the stalk rots is multi-faceted. First, choose hybrids with the best resistance available. Hybrids that also have good resistance to foliar diseases will also offer an advantage when managing stalk rot, as fo-liar disease can stress corn plants and lead to increased risk of stalk rots like anthracnose stalk rot. Cultural practices such as crop rotation and tillage to manage surface residue can also help. Other practices that reduce plant stress such as balanced fertilization, proper planting population, providing suitable drainage, and using well adapted hybrids for your location will reduce the risk of anthracnose stalk rot.

Fungicides are not recommended for managing stalk rots, directly. However, we have observed better standability of corn in years with heavy foliar disease pressure, where fungicides have been applied. This makes sense, because controlling heavy foliar disease allows the plant to continue to produce car-bohydrates through photosynthesis. When heavy foliar disease pressure is left unchecked, corn plants can scavenge the stalks for resources predisposing corn plants to stalk rot diseases and a loss in stalk integrity.

What corn ear rots and mycotoxins should I watch out for?

With all the wet weather, several ear rots have appeared in corn around much of the state. Ear rots caused by fungi in the groups Diplodia (Fig 2.), Fusarium, and Gibberella (Fig. 2) will be the most likely candidates to watch for as you begin harvest. Fusar-ium and Giberrella are typically the most common fungi on corn ears in Wisconsin. This group of

fungi not only damage kernels on ears, but can also produce toxins called mycotoxins. These toxins

(fumonisins and vomitoxin) can threaten livestock that are fed contaminated grain. Thus grain buyers actively test for mycotoxins in corn grain to monitor mycotoxin levels to be sure they are not above certain action levels established by the U.S. Food and Drug Administration (FDA).

The FDA has established maximum allowable levels of fumonisins in corn and corn products for human consumption ranging from 2-4 parts per million (ppm). For animal feed, maximum allowable fumonisin levels range from 5 ppm for horses to 100 ppm for poultry. Vomitoxin limits are 5 ppm for cattle and chickens and 1 ppm for human consumption.

Diplodia ear rot is not as common in Wisconsin. This disease is often more severe in years where dry weather precedes silking, followed by wet weather immediately after silking. Diplodia ear rot does not produce mycotoxins. While this disease does not result in mycotoxin accumulation, it can cause grain yield loss and quality issues.

Figure 2. Diplodia ear rot (2 ears on the left) and Gibberella ear rot (2 ears on the right) of corn. Photo Credit: Craig Grau.

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For more information about ear rots and to download a helpful fact sheet pro-duced by a consortium of U.S. corn pathologists, CLICK HERE.

How do I reduce mycotoxin risks at harvest?

Before harvest, farmers should check their fields to see if moldy corn is present. Sample at least 10-20 ears in five locations of your field. Pull the husks back on those ears and observe how much visible mold is present. If 30% or more of the ears show signs of Gibberella or Fusarium ear rot then testing of harvest-ed grain is definitely advised. If several ears show 50-100% coverage of mold testing should also be done. Observe grain during harvest and occasionally inspect ears as you go. This will also help you determine if mycotoxin testing is needed.

If substantial portions of fields appear to be contaminated with mold, it does not mean that mycotoxins are present and vice versa. Remember, Diplodia ear rot does not produce mycotoxins. However, if you are unsure, then appropriate grain samples should be collected and tested by a reputable lab. Work with your corn agronomist or local UW Extension agent to ensure proper samples are collected and to identify a reputable lab. If tests show high levels of myco-toxins in grain, that grain SHOULD NOT BE BLENDED with non-contaminated corn.

For more information on mycotoxins and to download a fact sheet, CLICK HERE.

Helpful information on grain sampling and testing for mycotoxins can be found by CLICKING HERE.

For a list of laboratories that can test corn grain for mycotoxins, consult Table 2-16 in UW Extension publication A3646 – Pest Management in Wisconsin Field Crops.

How should I store corn from fields with ear rots and mold?

If you observe mold in certain areas of the field during harvest, consider harvesting and storing that corn separately, as it can contaminate loads; the fungi causing the moldy appearance can grow on good corn during storage. Harvest corn in a timely manner, as letting corn stand late into fall promotes Fusarium and Gibberella ear rots. Avoid kernel damage during harvest, as cracks in kernels can promote fungal growth. Also, dry corn properly as grain moisture plays a large role in whether corn ear rot fungi continue to grow and produce mycotoxins. For short term storage over the winter, drying grain to 15% moisture and keeping grain cool (less than 55F) will slow fungal growth. For longer term storage and storage in warmer months, grain should be dried to 13% moisture or less. Fast, high-heat drying is preferred over low-heat dry-ing. Some fungi can continue to grow during slow, low-heat drying. Also, keep storage facilities clean. Finally, mycotoxins are extremely stable compounds: freezing, drying, heating, etc. do not degrade mycotoxins that have already accumulated in grain. While drying helps to stop fungal growth, any mycotox-ins that have already accumulated prior to drying will remain in that grain. The addition of acids and reducing pH can reduce fungal growth but will not affect mycotoxins that have already accumulated in harvested grain.

For wet corn, earlage, snaplage or corn silage, promote optimal fermentation to preserve and stabilize the feed for dairy or beef cattle. As mentioned above, mycotoxin presence will not be alleviated, however stabilizing the crop can en-

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sure the issue won’t worsen. Seal the crop as quickly as possible after harvest and use a research proven bacterial inoculant, acid or chemical preservative to stabilize the crop quickly after sealing. Monitor bag, bunker, and pile silo plas-tic for holes throughout the year and seal those you find quickly. Seal the ends and/or edges with added weight to minimize air infiltration into the silage or grain.

For more information on properly storing grain and to download a fact sheet on the subject, CLICK HERE.

What impact will ear and stalk rot have on my cows?

Ear and stalk rots do not equate to animal health issues, however mycotoxins or wild yeast contamination which may be produced by or accompany ear and stalk rots can affect rumen health and digestion. As described above, manage the crop to the best of your ability from harvest through storage. Upon feed out, introduce heavily ear and stalk rot-laden feeds slowly into the ration. Test the suspicious crop for mold, yeast and vomitoxin content as you begin feed-ing it and closely monitor dry matter intakes and animal health.

If animal health issues or contaminant levels for yeast and mycotoxin are rec-ognized, consult with your nutrition and veterinary advisor as to the best plan of attack. Dilute the suspicious feed to a lesser amount if possible or consider research backed nutritional additives which can lessen yeast or mycotoxin impact on health.

WISCONSIN FRUIT NEWS ISSUE 14CHRISTELLE GUEDOT, FRUIT CROP ENTOMOLOGY AND EXTENSION SPECIALIST, WISCONSIN-MADISON FRUIT PROGRAM

Apple maturity levels are still running 6-8 days later than normal due to cool, wet weather at the Peninsular Agricultural Research Station. However, this week’s five-days straight of sunny days and cool nights will go a long way in fully maturing most varieties.

This week the Atucha Lab did an analysis of the grape varieties sent from the Peninsular Agriculture Research Station.

All grape cultivars at WMARS have been harvested. See the Brix, TA and pH levels in the Grape Variety Fruit Maturation Evaluation.

Grape Scouting Report: Social wasps are still here.

Overall caseload at the UW Insect Diagnostic Lab has begun to decrease for the year, including reports of fruit crop insects.

Bitter rot was found in samples analyzed by UW-Madison/Extension Plant Dis-ease Diagnostic Clinic.

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2020 IPM FIELD SCOUT TRAINING CLASSBRYAN JENSEN, UW EXTENSION AND IPM PROGRAM

The Madison Field Scout Training Class (354) will be held on the UW Madison Campus from January 6-10, 2020. The course is designed to provide the skills necessary for proper pest identification, crop scouting techniques as well as provide complimentary baseline information for people preparing for the state CCA exam. Additional information such as crop growth and development, pest life cycle, pest damage symptoms and economic thresholds will be covered. Pest control recommendations, although discussed, will not be highlighted in detail during this course. Crops covered will include, corn, alfalfa, soybean and wheat. Click here for the course syllabus.

Non-student registration fee is $225/person but does not cover campus parking. Online registration (preferred) for the Field Crop Scout School can be made at the PAT Store. Checks should be made payable to University of Wis-consin-Madison and sent to Bryan Jensen, Dept. of Entomology, 1630 Linden Dr., Madison, WI 53706.

Online registration can be found by clicking here.

For more information on this course, please contact Bryan Jensen at:

Dept. of Entomology

1630 Linden Dr.

Madison, WI 53706

(608) 263-4073

bmjense1@wisc.edu

PLANT DISEASE DIAGNOSTIC CLINIC (PDDC) UPDATEBRIAN HUDELSON, SUE LUELOFF, ALEX MIKUS AND ANN JOY

The PDDC receives samples of many plant and soil samples from around the state. The following diseases/disorders have been identified at the PDDC from October 5, 2019 through October 11, 2019.

Table attached at the end of newsletter or

View table of diseases/disorders here: https://dtk9tvco613fv.cloudfront.net/wp-content/uploads/sites/39/2019/10/FullTable101119.pdf

SOYBEAN MIDGE UPDATEBRYAN JENSEN, DEPT. OF ENTOMOLOGY AND DIVISION OF EXTENSION

A new species of midge has been found in a single NW Wisconsin soybean field. Note, this is not the soybean gall midge (SGM) I have written about earlier

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but a different species that is very similar in appearance but not consid-ered an economic pest.

This new species is Karshomyia cau-licol (Gagne’). I am not sure what the common name will eventually be, but people are referring to is as the white mold gall midge (WGM). As best as we know right now, it does not cause white mold, nor does it predispose a plant to white mold. Likely, it is feed-

ing on decaying plant tissue.

WGM larvae are very similar in appearance SGM larvae which are an economic pest in parts of NE, ND, IA, MN and MO. By the way, SGM’s geographic range has increased during the 2019 growing season but not yet found in Wiscon-sin. The larvae of both species are small, and most individuals have an orange coloration with varying degrees of color intensity. What you will find useful to differential between the two species will not be the larvae themselves but rather when, where and how they are feeding.

SGM can damage a wide range of plants from the very early vegetative stag-es (V3) to late reproductive soybeans. However, the majority (if not all) the damage is at or near the soil line. A blackened epidermis is often found at the feeding site. Above ground plant symptoms range from unthrifty to dead plants. Often, individual plants will have brittle stems that may break at the soil line. WGM feeding has been found primarily at the end of the growing season. Feeding sites are usually above ground and can be associated with previous tissue damage. SGM damage is usually more severe at the field edge. WGM may be found throughout the entire field.

Please understand what we know is very limited at this point and likely will change. We certainly will be getting more information out later. In many respects, I am glad it is October. It will give all of us time to sort out what is happening, organize some thoughts and prepare for 2020.

Many thanks to Ryan Bates, Pioneer, for finding and submitting the WGM sam-ple. We all appreciate your help.

WGM larvae circled in red

UW-Madison/Extension Plant Disease Diagnostic Clinic (PDDC) Update

Brian Hudelson, Sue Lueloff, Alex Mikus and Ann Joy The PDDC receives samples of many plant and soil samples from around the state. The following diseases/disorders have been identified at the PDDC from October 5, 2019 through October 11, 2019.

PLANT/SAMPLE TYPE

DISEASE/DISORDER PATHOGEN COUNTY

BROAD LEAFED WOODY

ORNAMENTALS

Catalpa Verticillium Wilt Verticillium sp. Eau Claire

Mountain-Ash (Korean)

Fire Blight Erwinia amylovora Brown

Oak (Bur) Anthracnose

Bur Oak Blight

Tubakia Leaf Spot

Discula sp.

Tubakia iowensis

Tubakia dryina

Waukesha

Dane

Dane, Rock, Waukesha

Oak (Red) Anthracnose

Monochaetia Leaf Sport

Oak Wilt

Discula sp.

Monochaetia sp.

Bretziella fagacearum

Columbia

Columbia

Columbia

Oak (White) Anthracnose

Septoria Leaf Spot

Tubakia Leaf Spot

Discula sp.

Septoria sp.

Tubakis dryina

Columbia, Crawford, Milwaukee

Columbia, Crawford

Columbia, Milwaukee

FIELD CROPS

Corn Anthracnose

Common Rust

Eyespot

Gray Leaf Spot

Northern Corn Leaf Blight

Northern Corn Leaf Spot

Southern Rust

Tar Spot

Colletricum graminicola

Puccinia sorghi

Kabatiella zeae

Cercospora sp.

Exserohilum turcicum

Bipolaris zeicola

Puccinia polysora

Phyllachora maydis

Washington

Washington

Pierce

Washington

Pierce, Washington

Pierce

Pierce

Washington

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PLANT/SAMPLE TYPE

DISEASE/DISORDER PATHOGEN COUNTY

FIELD CROPS (Continued)

Soybean Brown Stem Rot

Charcoal Rot

Sudden Death Syndrome

Phialophora gregata

Macrophomina phaseolina

Fusarium virguliforme

Dodge, Shawano

Dodge

Dodge

FRUIT CROPS

Apple Root/Crown Rot Pythium sp., Fusarium sp. Richland

Cranberry Blotch Rot Physalospora vaccinii Wood

Grape Anthracnose

Black Rot

Sphaceloma ampelinum

Phyllosticta ampelicida

Oneida

Oneida

HERBACEOUS ORNAMENTALS

Zinnia Alternaria Leaf Blight Alternaria zinnae Portage

NEEDLED WOODY ORNAMENTALS

Spruce (Blue) Rhizosphaera Needle Cast Rhizosphaera kalkhoffii Waukesha

VEGETABLE CROPS

Cabbage (Red) Black Rot Xanthomonas campestris pv. campestis

Winnebago

Carrot Alternaria Leaf Blight

Cercospora Leaf Spot

Alternaria dauci

Cercospora carotae

Portage

Portage

Corn (Sweet) Common Rust

Tar Spot

Puccinia sorghi

Phyllachora maydis

Rock

Rock

Potato (Tuber) Bacterial Soft Rot

Fusarium Dry Rot

Late Blight

Pectobacterium carotovorum subsp. carotovorum, Pectobacterium atrosepticum

Fusarium sp.

Phytophthora infestans

Marquette

Marquette

Adams, Barron, Waushara

Snap Bean Black Root Rot

Fusarium Root Rot

Rhizoctonia Root Rot

Thielaviopsis sp.

Fusarium sp.

Rhizoctonia sp.

Lafayette

Lafayette

Lafayette

Squash (Butternut) Powdery Mildew Oidium sp. Vernon

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PLANT/SAMPLE TYPE

DISEASE/DISORDER PATHOGEN COUNTY

VEGETABLE CROPS

(Continued)

Watermelon Downy Mildew

Plectosporium Blight

Powdery Mildew

Pseudoperonospora cubensis

Plectosphaerella cucumerina

Oidium sp.

Columbia

Columbia

Columbia

SPECIALTY CROPS

Hemp (Industrial) Root/Crown Rot Fusarium sp. Dane

For additional information on plant diseases and their control, visit the PDDC website at pddc.wisc.edu. Follow the clinic on Facebook and Twitter @UWPDDC.

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