MSU Extension Vegetables

Weather

This past winter was the warmest on record with an average December – February temperature over 10 degrees Fahrenheit above-normal. Soil temperatures were also warmer than normal. Degree day totals (base 50 F) are roughly one calendar week ahead of normal for most of Michigan.

This week’s forecast features:

• Sunny to the north, decreasing clouds to the south and colder on Wednesday, April 24. Fair with widespread frost and freezing temperatures overnight. Fair and dry Thursday. Warmer with rain redeveloping southwest-northeast Friday afternoon and continuing into Saturday morning. Rain likely once again Sunday into Monday.
• High temperatures in the 40s Wednesday, warming back to the 60s in the north to 70s in the south this weekend. Low temperatures in the upper teens in the north to the 20s to low 30s south Thursday with frost and freezing temperatures. Scattered frost is also possible Friday morning. Lows warming back to the 40s and 50s again this weekend.
• Precipitation totals of 1-1.5 inches through next Wednesday.
• Medium range outlooks generally call for above normal mean temperatures and precipitation totals the next one to two weeks. New long lead outlooks call for warmer than normal mean temperatures for the remainder of the spring season into the upcoming summer months.

Crop updates

With regular rains, preemergent herbicide activation has not been as much of an issue as observed last spring. Keep in mind the role that soil type plays in efficacy of soil-applied herbicides. Percent organic matter and cation exchange capacity vary based on soil types and strongly influence residual activity degradation of herbicides. Check out the Michigan State University Extension article “Determining soil type important for successful preemergent weed control” for better understanding. Be sure to consult your herbicide label for specific rates in different soil types.

Are you a grower that plants “a little of this and a little of that” on plastic mulch? Maintaining weed management across several crop species can be a chore with herbicides. Dual (s-metolachlor), Treflan (trifluralin), Prowl (pendimethalin) and Sandea (halosulfuron) are the most widely labeled herbicides you could use between the plastic beds as preemergence herbicides. But, none of them are labeled for all vegetables, and they each have gaps in what they will control. Further, trifluralin and pendimethalin both require incorporation.

With this in mind, it may be worth looking into mechanical means for stirring soil between the beds for incorporation or for weed control itself. Finger weeders and spiders can pull or throw soil onto the buried strip of plastic on either side of the bed without tearing it so much, while multivators and various shovels can work the middles. You can run these tools while plants are still small or while the beds are lying in wait for transplants.

It’s important to match your weed management tool with your bed-laying tool or planter so that you can follow the waves of wandering beds. Much of this advice applies to baresoil crops as well, but even more tools are available in these settings, such as rolling baskets and tine harrows.

Asparagus

There was lots of activity in west central Michigan last week as many growers applied fertilizer, sprayed glyphosate to terminate the rye, mowed and applied preemergent herbicides. In some locations, early emerging spears may have been mowed off, but thankfully these were likely the first uneven picking. Our Michigan State University (MSU) asparagus emergence model (based on soil temperatures at the West Central Michigan Research and Extension Center in Hart) predicts we will hit the threshold for asparagus emergence (25% of crowns with at least one spear greater than 1 inch) in Hart in the next few days (Figure 1). However, actual emergence will vary based on region, soil type, ground cover and variety. Emergence is typically delayed one to three days in fields that had a thick rye cover crop. Some cultivars (e.g., ‘Sequoia’) are also known to emerge earlier. 

Just a reminder that chlorpyrifos is legal to use this year. Historically, this application has targeted cutworms.

Brassicas and greens

Transplants of cabbage and other brassicas have been going in since early April. Many growers are holding out this week for more transplanting until tomorrow’s freeze passes.

For cabbage maggot, remember that chlorpyrifos is temporarily legal to use in 2024, and any resulting crops will be legal to sell. If you have a stock of chlorpyrifos, it is a good time to use it or lose it. The Environmental Protection Agency (EPA) is expected to publish a new rule that will once again ban use in all but 11 crops, which do not include brassicas. Verimark is consistently effective when applied as a tray drench to transplants. The label specifies the drench must occur within 72 hours of planting. This application will also provide early flea beetle and caterpillar control.

Many organic growers know that row cover is highly effective for cabbage maggot control. Just make sure you are not planting onto ground that had brassicas later last year (where flies may be overwintering). 

Carrots and celery

Carrot sowing began last week in west central Michigan and celery transplanting has been ongoing or is just starting, depending on the farm. Similarly, in the east side of the state, carrot and celery have started being planted.

Fruiting vegetables

Lots of field work and herbicide burndowns are taking place when weather permits. Plastic has been laid on some farms. Greenhouses are fired up with transplants. During this late spring time as transplants are being held for the field, fungal pathogens can become an issue, especially if the weather remains overcast. As the transplants are being held in the greenhouse, it’s important to monitor watering closely so that the plants are not overwatered, which could exacerbate fungal disease problems. Botrytis gray mold can be opportunistic and infect the cotyledons as they senescence along with the lowermost foliage, especially when the transplant canopy begins to close, restricting air movement among the plants.

Greenhouse growers should be on the lookout for bacterial problems, especially on tomato and pepper transplants. Growers of tomato transplants should be scrutinizing plants carefully as they leave the greenhouse to ensure that bacterial symptoms (see descriptions below) are not evident.

Bacterial speck on tomato is probably one of the easiest bacterial diseases to identify. Small, dark brown spots occur on the leaves with each spot surrounded by a yellow halo. Typically, just a few plants within a flat show symptoms initially. Although bacterial speck may not produce the panic that the other bacterial diseases do, speck can result in significant yield losses if the blossoms become infected.

Bacterial spot on tomato is not as easy to identify as bacterial speck. Bacterial spot results in larger spots or blotches on the leaves and stems than bacterial speck. The spots may have tan centers and are a maximum of 0.25 inches in diameter. If the infection is severe, the entire leaf turns yellow and eventually drops off of the plant. In previous years, growers in Michigan have experienced significant yield losses and devastating fruit spotting due to bacterial spot.

Bacterial canker has been a problem in previous years and should not be overlooked.  Symptoms appear different than those associated with bacterial speck and spot and include small, tan, blister-like lesions on the leaves. Symptoms progress to include brown streaking on the petioles and stems.

Plants showing symptoms of bacterial disease should be immediately removed from the greenhouse and destroyed. In addition, plants immediately adjacent to those showing symptoms should also be removed and destroyed. This ensures removal of plants that are contaminated with the bacteria but not yet showing symptoms. If the affected flat is not immediately removed from the greenhouse, the disease will spread to nearby healthy transplants.

Unfortunately, if the disease begins in a flat that is too far from the walkway to be seen easily, the disease may go undetected until several flats are severely infected. Although epidemics may seem to appear overnight, chances are it had rather humble beginnings in just a few plants and simply progressed unnoticed for a couple of weeks. Plug sheets containing infected plugs should not be reused.

Fungicides registered for control of bacterial diseases on vegetable transplants in the greenhouse. Streptomycin (Agrimycin) plus copper has historically been used for controlling bacterial diseases in the greenhouse. Copper products registered for use on tomatoes in the greenhouse vary in the amount of metallic copper that is available for pathogen control. Products that have a higher amount of metallic copper include Kocide O, Nordox 75WG and Badge. Generally, products with a higher metallic copper content tend to have a longer reentry period ranging from 12 to 48 hours. Those with significantly less metallic copper may have a shorter reentry time but may not be sufficient to limit bacterial issues under favorable greenhouse conditions.

Although growers have relied on streptomycin (Agrimycin) plus copper for disease control, there has not been uniform success in halting the spread of bacterial diseases with this spray program. Rather, some of the most significant plant losses in the last few years due to bacterial diseases have occurred despite regular, preventive applications of streptomycin plus copper.  Bouts of cloudy weather resulting in high humidity coupled with splashing occurring during watering will certainly give the edge to the bacterial pathogens.

Transplants must be removed

Removing infected transplants from the greenhouse is the most critical component of managing bacterial diseases once they’ve been detected. In addition to removing plants with symptoms, it is recommended that the flats of transplants adjacent to the symptomatic plants also be disposed of even though they appear to be healthy. This is important because it is likely that the bacterial pathogen has been splashed to the plants adjacent to those with disease symptoms. Planting diseased transplants into the field ensures the disease is established early with the greatest potential for yield and quality reduction if the weather favors disease.

It is also unrealistic to expect fungicides such as coppers or streptomycin (Agrimycin) to cure these diseases. Watching tomato transplants carefully, learning to recognize disease symptoms, obtaining a solid diagnosis if problems occur and immediately removing diseased plants is a disease management strategy that affords growers some degree of protection against these bacterial diseases.

Troubleshooting is an ongoing process in transplant greenhouses. Beyond the bacterial symptoms mentioned above, white or bleached leaves on transplants is often a sign of cold injury. Prolonged periods below 55 F can cause chilling damage on warm-season crops like tomatoes or peppers. Symptoms similar to cold damage can also be a result of sulfur dioxide (SO₂) toxicity. Like ethylene, sulfur dioxide occurs in exhaust from greenhouse heaters. If not vented properly, SO₂ may accumulate in the greenhouse, causing leaf burn on sensitive young seedlings. Routine heater maintenance is important for preventing build-ups of pollutants in the transplant growing space.

Onions

Direct seeding started in mid- to late March and early April. Some farms are done sowing, and some plants are up, with some advanced fields in the flag stage. Onion sets and plants are being transplanted.

Root crops and potatoes

Potatoes are around 60% planted in southwest Michigan. Some beets and radishes are planted in the east and west side of the state. Turnip, radish and parsnip sowing has been ongoing outdoors. Early turnips had one true leaf earlier this week.

Cabbage maggot is a concern for brassica root crops. Remember that chlorpyrifos is temporarily legal to use for cabbage maggot in 2024, and any resulting crops will be legal to sell. If you have a stock of chlorpyrifos, it is a good time to use it or lose it, as this window for legal use is only temporary. The EPA is expected to publish a new rule that will once again ban use in all but 11 crops, which do not include brassica root crops. Granular chlorpyrifos has been hard to come by, leaving growers with liquid options. If using an EC formulation, make sure to read the label section (and talk with crop consultants) about compatibility with liquid fertilizers.

Other at-plant options: Verimark is labeled for use in-furrow for cabbage maggot in brassica root crops, however we have not found it to be consistently effective in past trials. Diazinon is labeled for radish and rutabaga, but not turnips.

Sweet corn

Sweet corn planting has begun for early markets, with some early plantings starting to germinate.

Sweet corn growers have many corn herbicides available to them, with varying potentials to carry over. Many are premixes of multiple herbicides, and confusingly some products with similar trade names, have slightly different mixes. For example, Accuron contains four active ingredients including atrazine while Accuron Flexi has all three minus the atrazine. All this means it’s necessary to be intentional about what herbicides you use this year, keeping in mind the possibility for carryover to impact the next crop. Bottom line: Check the label for rotational restrictions.

Strawberries

Flower trusses have begun emerging. Growers are looking at early season herbicides to control overwintering weeds. When selecting an herbicide, check the preharvest interval.

Events 

• April 25, 7-8 a.m., Field Crops Virtual Breakfast Series: Conservation Practices
• April 30, Shiawassee County Pesticide Applicator Training
• May 2, 7-8 a.m., Field Crops Virtual Breakfast Series: Staging Crop Growth Stages
• May 7-8, 2024 Agritourism Summit and Pre-Summit Farm Tour
• May 9, 7-8 a.m., Field Crops Virtual Breakfast Series: Managing Corn and N After Waterlogging
• May 13, St. Joseph County Pesticide Applicator Training
• May 15, Hillsdale County Pesticide Applicator Training
• May 16, 7-8 a.m., Field Crops Virtual Breakfast Series: Post Weed Control Management
• May 23, 7-8 a.m., Field Crops Virtual Breakfast Series: Dry Bean Planting Options
• May 30, 7-8 a.m., Field Crops Virtual Breakfast Series: Wheat Fungicide Recommendations
• May 31, Oakland County Pesticide Applicator Training
• June 6, 7-8 a.m., Field Crops Virtual Breakfast Series: Sprayer Setup
• June 8, 9 a.m.-4 p.m., Soil and Composting Field Day
• June 11, 6:30-8 p.m., Western Lake Erie Basin State of the Lake Meeting: Lenawee County
• June 13, 7-8 a.m., Field Crops Virtual Breakfast Series: Irrigation Management
• June 13, 6:30-8 p.m., Western Lake Erie Basin State of the Lake Meeting: Monroe County
• June 18, 6:30-8 p.m., Western Lake Erie Basin State of the Lake Meeting: Hillsdale County
• June 19, 9 a.m.-1:30 p.m., Food-Grade Grains Field Day
• June 20, 7-8 a.m.,Field Crops Virtual Breakfast Series: Wild Weather for Hay
• June 27, 7-8 a.m., Field Crops Virtual Breakfast Series: Insect Update Beneficials & Corn Borer
• July 11, 7-8 a.m., Field Crops Virtual Breakfast Series: Cercospora for Sugarbeets
• July 18, 7-8 a.m., Field Crops Virtual Breakfast Series: White Mold - Tar Spot Spraying – Will it Pay?
• July 25, 7-8 a.m., Field Crops Virtual Breakfast Series: Hot Topics Q&A Session
• Aug. 1, 7-8 a.m., Field Crops Virtual Breakfast Series: Cover Crops After Wheat
• Aug. 8, 7-8 a.m., Field Crops Virtual Breakfast Series: MSU Diagnostic Lab Topics
• Aug. 15, 7-8 a.m., Field Crops Virtual Breakfast Series: Field Crops Nematode Update
• Aug. 22, 7-8 a.m., Field Crops Virtual Breakfast Series: Lime Recommendations for Field Crops
• Aug. 29, 7-8 a.m., Field Crops Virtual Breakfast Series: Maximizing Wheat Yield Potential
• Sept. 5, 7-8 a.m., Field Crops Virtual Breakfast Series: Drought-Proofing Agriculture with Drainage Water Recycling
• Sept. 12, 7-8 a.m., Field Crops Virtual Breakfast Series: Grain Marketing
• Sept. 19, 7-8 a.m., Field Crops Virtual Breakfast Series: Late Season Weed Control

This work is supported by the Crop Protection and Pest Management Program [grant no. 2021-70006-35450] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.