Introduction to Using Mustard Cover Crops for Biofumigation in Pumpkin

This article is an introduction to the general processes and basic steps of how to use mustard cover crops to reduce soil borne diseases, such as Plectosporium, in pumpkin. Research using mustard plants to naturally biofumigate soil to allow for more normal yield and fruit quality, has been conducted in several states and Canada, sometimes with mixed results. The results of this trial will be released in a report later in the season.

Mustard cover crop in full bloom.

The field intentionally selected for this trial was cropped to pumpkin in 2018 and exhibited high amounts of Plectorsporium infections on both plant and fruit. The general recommendation for a field infested with this disease would be to rotate away from cucurbits for 3-5 years. Instead of rotation, we are investigating the use of biofumigation as a means to reduce disease incidence.

In mid-April when conditions were suitable for direct seeding, Pacific Gold (6lb/A), Caliente 199 (10lb/A), and a 50/50 blend of the two were drilled into plots at the Western Ag Research Station in South Charleston. Prior to seeding, 100 lb/A of urea and 34 lb/A ammonium sulfate were broadcast and incorporated to increase the biomass and glucosinolate levels of the cover crop. Glucosinolates are the compounds responsible for the biofumigation effect and are released when the mustard plant tissue is macerated and incorporated into the soil. The production of these compounds peak during flowering.

Once peak bloom has been reached it is necessary to mow the plants, immediately followed by incorporation (such as rototilling), packing, and then sealing the soil with water. Once these steps have been performed, the glucosinolates are broken down into other compounds in the soil such as isothiocyanates, where they begin the biofumigation reactions. It is recommended to wait 7-10 days after incorporation to either direct seed or transplant. We seek to confirm the necessity of the waiting period by both seeding and transplanting pumpkins one day after incorporation; we’ll report if any negative effects are seen on the germination rate or growth of the transplants.

To hear more details about the trial and see all steps including the incorporation of mustard cover crop, watch this video posted to the OSU IPM YouTube channel: https://youtu.be/Taz-PhDphhA

If you have worked with mustard cover crops before and have any experiences positive or negative to share, please send them to me at jasinski.4@osu.edu.

Make a Withdrawal from your Soil Weed Seed Bank: Stale Seedbank Technique

Ah spring!  The war against weeds begins anew. The first major skirmish of the growing season should happen before planting. The stale seed bed technique is an often over-looked practice that can be used before planting. It works by first encouraging weeds to sprout and then killing them when they are young and most vulnerable. For organic growers, a stale seed bed can replace the effects of a pre-emergence herbicide. And when used properly, it can contribute to both short-term and long-term weed management.

Weed control can be handled with short-term or long-term approaches. Short-term management focuses on controlling weeds during the first part of crop growth when weeds are more likely to affect crop yields. Long-term weed management, however, works all season-long to deplete weed seeds from the seedbank (the reservoir of viable weed seeds in the soil). Whichever approach you take, using a stale seed bed is a great cultural weed control technique.

To use the stale seed bed most effectively, start several weeks before planting. An initial cultivation kills any emerged weeds that have overwintered. It also brings weed seeds to the surface where exposure to light and oxygen stimulate germination. Depending on the weather and types of seeds present in the soil, weeds may sprout up overnight or over a few weeks. When weeds have germinated and are still small and young, they are easy to kill with a second light cultivation. This process is then repeated as needed and as time allows. As few as three cycles of light/ shallow tillage can reduce the number of subsequent weeds noticeably. For fields and gardens with very heavy weed infestations more cycles of repeated tillage over a few years will be needed. Using a stale seed bed may push back your planting date; but in the absence of weed competition, the crop will have more access to water and sunlight and be able to make up for lost time.

Keys to Success

  • Do not allow emerged seedlings to grow large. It is best to till lightly just as the first seedlings are emerging as this and the earlier ‘white thread’ stage are the most susceptible to desiccation. The more time new weeds have to develop roots, the harder they become to kill with a shallow cultivation.
  • Keep the cultivation shallow to avoid bringing new weed seeds to the surface. The implement used to stir the soil should not go deeper than 2 inches with most of the stirring in the top inch.
  • The technique is dependent upon having adequate soil moisture. Under drought conditions preparation of a stale seedbed may require irrigation to stimulate weed seed germination.
  • Deeper initial tillage can be used to bury an existing weed problem. Tillage, especially when done with a disc or a power tiller, distributes the previous year’s weed seeds throughout the top 6 inches or so of soil. In contrast, an inversion tillage that turns sod upside down will place last year’s seeds 6 inches or so under the surface. From there they are unlikely to emerge unless further discing or lighter tillage moves them closer to the surface. Used skillfully, a deep inversion plowing followed by stale seed bed can put a serious surface weed problem out-of-sight and out-of-mind, at least until the next time the field is plowed deeply.

Stale Seedbed is most effective when it is part of a zero weed threshold system.

The common short-term approach to managing weeds, (weed scientists usually call this the “critical period approach”) is to control weeds aggressively during the first 4-6 weeks after the crop is planted. This 4-6-week period is the critical period during which crops stands are established and yield is secured. Afterwards weeds are of less threat to production; therefore, many farmers scale back control efforts. However, weeds that grow before and after the critical period are still a problem. If allowed to flower and set seed, they will be planting a future crop of weed problems. A long-term approach to weed management, called zero weed seed threshold, requires constant diligence and removal of all weeds before they produce seeds–even after harvest. Research indicates that 3-4 years of using this approach will result in a field with relatively few weeds, provided weed seeds are not introduced from without the field (in seed, irrigation water, on equipment, etc.).

Both short-term and long-term approaches have benefits and drawbacks, many of which depend on a farmer’s individual goals, crops, and available resources. A new online tool from Ohio State allows farmers to think through various weed control approaches in the context of their own individual situations. For those looking to make changes to their weed management, the Organic Weed Decision Making Tool, shows pros and cons of various strategies over time and gives steps to implementing new tactics. Learn more at go.osu.edu/eco-weed-mngt.

More and Better Tools to Help Respond Effectively to Weather-related Challenges

A vegetable farmer pointed out to me recently that “rain” is a four-letter word and that like other ones, he likes rain to fall in just the right amount and at just the right time. Well, although we can’t control when, where, or how much rain will fall, many people in agriculture and the area known as climate services are working to develop reliable forecasts of and effective responses to current and future weather.

Shared commitments to that goal were evident throughout the recent Climate Services Summit (https://climate.osu.edu/news/byrd-center-hosts-ohio-climate-services-summit) coordinated by the State Climate Office of Ohio based at The OSU (https://climate.osu.edu/). Just as important, steps to providing farmers and others with better decision-aids also became clearer through discussions at the program. Ohio State University Extension contributes to the process – for example, see resources, programs, and input offered by Aaron Wilson, Jason Cervenec, and John Fulton – and addressing weather-related challenges and needs of vegetable growers will be important going forward. These were summarized well in two recent reports (https://www.climatehubs.oce.usda.gov/archive/sites/default/files/Midwest_Climate_And_Specialty_Crops_2015_508.pdf and https://store.extension.iastate.edu/product/15448) but more input is always welcome.

Throughout much of this field planting season, many have needed to scramble, improvise, and work round the clock to get work done as weather, soil, labor, and other conditions allowed. It seems that most have experienced the dark side of their share of passing fronts, with few farms experiencing clear skies and calm winds for extended periods. Overall, this seems consistent with information in http://glisa.umich.edu/media/files/GLISA%202%20Pager%202019.pdf (GLISA also participated in the recent Summit). Field and high tunnel plantings have been affected in their own ways by recent conditions, although it is fair to say that most high tunnel plantings were able to remain on schedule, an important early step toward a successful season. Ideally, we will soon see that high tunnels are just one of many key tools available to help maintain and enhance vegetable production amidst changing and increasingly extreme conditions.

Spotted-wing Drosophila are slowly becoming active

Since 2012, Extension educators and a handful of state specialist have set out traps to monitor when spotted-wing Drosophila (SWD) begin to migrate from their overwintering locations into cultivated small fruit fields where growers have to actively manage them. This year, only two counties, Franklin and Greene, have traps out early to monitor for this pest ahead of the dozen or so county network sites that will become active in mid-June.  Franklin county has caught 26 SWD in 2019 but only back in January, nothing more recent. The Greene county site caught two SWD last week (May 28), one in a wood line and one at the edge of a blueberry field but none this week. Recall that the threshold is one fly to begin management when the fruit begins to ripen or is ripe. So, the message is the adults are slowly becoming active, and as the weather warms and fruit begins to ripen, be on the lookout for SWD.

For tips on how to identify, monitor, and manage SWD, check out OSU’s resources at http://u.osu.edu/pestmanagement/pests/swd/and the SWD section of OSU’s IPM YouTube channel https://www.youtube.com/channel/UCzcWaLH3mx7HUKh4OF7bYPA

Research newly Completed and Started

High tunnel studies are affected by weather. However, typically, high tunnel work continues when some operations in open field production are halted. Like growers, the Vegetable Production Systems Lab (VPSL is transitioning to full “summer mode” as conditions allow. See the six panels below for snapshots of a portion of our recent and near-term activities and don’t hesitate to contact us for more information or if we can assist another way.

Matt Kleinhenz (kleinhenz.1@osu.edu; 330.263.3810)

Five-year soil balancing project results

Another wet spring, and many farmers postpone field work awaiting drier conditions. Could improved drainage be obtained through the application of common gypsum? This is one of the claims made by many consultants and farmers who use a practice called soil balancing.

Ohio State’s five-year study on soil balancing has been mentioned in previous VegNet articles. The project involved multiple long-term field tests, as well as interviews and surveys to better document practices and beliefs surrounding soil balancing. Despite a lack of past research proving soil balancing’s effectiveness, we found that the practice is used heavily by organic and conventional farmers in our region to reduce weeds, and improve soil quality, crop quality, and yields. While we were unable to demonstrate improvements in crop yields or quality, we did see limited effects on soil quality and weed populations in some of our test sites during the final year of the study.

Defining Soil Balancing

Traditionally, soil balancing strives to keep base cations calcium (Ca), magnesium (Mg), and potassium (K) at a recommended ideal ratio (typically 64:10:5). Although long practiced by farmers, soil balancing is not recommended by most researchers and Extension educators. Our study indicated around half of organic corn growers in the Midwest used a soil balancing approach, but more than 75% of the Extension researchers we surveyed felt soil balancing had no scientific merit.

It’s true that most soil balancing studies done in the past 20 years have reported the practice had no effect on production. However, our research reveals several potential gaps in these studies. Consultants and farmers we interviewed commonly reported that soil balancing improved overall soil quality and structure, which led to improved drainage and reduced weeds. While farmers also reported improved yields and profit, it was generally not the first improvement they mentioned. Interviewees noted that these improvement often happened gradually over several years. In short, past research may not have captured long range positive effects. Most recent studies were short-term, lasting one or two years; were conducted in a greenhouse rather than field; focused only on improved yields; and were conducted on limited types of soils. (Chaganti and Culman, 2017)

We also found that many farmers pair cation balancing with other soil improvement practices such as cover crops and biostimulants. The goal, according to the “balancers” we spoke with, is to improve the physical and biological properties of the soil.

Field Testing

Using both on-farm and Ohio State research station sites, we collected data on soils, weeds, and crops, while applying a variety of soil amendments to change Ca:Mg ratios. We measured crop quality using Brix, color, size, and other characteristics specific to individual crops. Vegetable crops included tomato, butternut squash, cabbage, popcorn, and edamame. Agronomic field crop trials were conducted as well.

We were unable to document any treatment effect on yield or crop quality. In the last year of testing, we did see effects on weed populations (either lower weed populations overall or lower populations of foxtail on “balanced” soils) and on soil root resistance (indicating improved soil structure with higher Ca saturation). These effects appeared only on some fields, but they do support our hypothesis that the positive results of soil balancing are related to improvements in soil structure and drainage. We hope to continue monitoring these fields to see if results become more consistent over time.

Recommendations

For now, we are unable to officially encourage or discourage the use of soil balancing. The following recommendations are based on field trials and on the experience and advice of our stakeholder advisory committee.

  • Soil test data is critical to making informed decisions about what to apply. Some Ohio soils may already have large concentrations of Ca due to Ohio’s limestone bedrock.
  • Watch your pH if using lime. Gypsum is a better choice to change the Ca level without affecting pH and it also provides sulfur.
  • Soils with a CEC below 10 may develop deficiencies. In soils with a low holding capacity for cations, excess Ca can lead quickly to deficiency levels of K, and possibly Mg. We did work in fields with Ca saturations well above 80% and observed K deficiencies in the soil and vegetables in these situations.
  • Consider economic factors. The higher your CEC, the more time and amendments will be needed to increase the Ca:Mg ratio. At some point—depending on the amount of change needed and the value of your crop—using soil balancing becomes an expensive practice.
  • Any time you try a new practice, monitor the results. If possible, try using the new practice on only part of your farm and compare it with a similarly managed area to see if the new technique is making a positive contribution over time.

With widespread use of the practice, soil balancing is a pertinent area for research and cooperative education. Our team hopes to continue studying the practices and long-term effects of soil balancing on a larger variety of soils. Drawing on experiment data and the experience of farmers and consultants, we will work toward guidelines and toward a mutual understanding of soil balancing.

Read more about this study at the Soil Balancing Project Site or the Vegetable Production Systems Laboratory. This work is supported by Organic Agriculture Research & Extension funding grant no. 2014-51300-22331/project accession no. 1003905 from the USDA National Institute of Food and Agriculture.

 

Growers and Researchers continue to Study Grafted Vegetable Plants

In Ohio, full-time study of grafted vegetable plants as products (i.e., sources of income) and production tools began more than ten years ago. Much has been learned and the popularity of grafted plants continues to trend upward. However, growers and researchers continue to ask many large, detailed, and tough questions about the roles of grafted plants in commercial production going forward. “Do grafted plants pay?” may be the most often asked and significant question. This brief article cannot address that question definitively for all readers due to the specific circumstances of each farm, field, crop, planting, season, etc. However, peoples’ collective understanding of the pros and cons of using grafted plants and of conditions leading to a good return on investment after using them is improving. As it does, success with grafted plants improves and their use increases. Regardless, additional research is needed. The three panels below briefly summarize a portion of the vegetable grafting research underway in Ohio in 2019. Please contact us if you would like to learn more about this work and stay tuned to VegNet and other outlets for updates.

Matt Kleinhenz, ph. 330.263.3810, email kleinhenz.1@osu.edu

Insecticide update for vegetable and fruit crops

There have been a few insecticide registrations that have come through since previous updates this past winter (summaries from January are available with these links: https://cpb-us-w2.wpmucdn.com/u.osu.edu/dist/1/8311/files/2019/02/PAT_Jan2019_1-page-1hvqfhg.pdf and https://cpb-us-w2.wpmucdn.com/u.osu.edu/dist/1/8311/files/2019/02/Summary_Jan2019_1-page-22nf965.pdf ).

Torac and Apta from Nichino America both contain tolfenpyrad as the active ingredient; both are in IRAC’s mode-of-action group 21A. Since March 2019, new crops on the new Torac label are onions and other bulb vegetables, lettuce and other leafy vegetables, and celery and other leaf petiole vegetables. Torac controls thrips, aphids, leafhoppers, flea beetles, and some caterpillars. Since February 2019, new crops on supplemental labels for Apta are strawberry and other low growing berries, raspberries and other caneberries, and blueberries and other bushberries. Apta controls thrips, plum curculio, fruitworms, Lygus (tarnished plant bug), and suppresses spotted-wing Drosophila.

Versys is a new insecticide from BASF that contains afidopyropen as the active ingredient, which puts it in IRAC group 9D. On the initial label in October 2018, the target pests were only aphids, as controlled at a low rate of product. A newer label now includes control of whiteflies at a higher rate of product.

Exirel is now allowed on raspberries and other caneberries, as shown on a supplemental label from November 2018. Use on caneberries is with a 1-day pre-harvest interval, for control of spotted-wing Drosophila and adult root weevils. Exirel is from FMC, and contains cyantraniliprole as the active ingredient, in IRAC group 28.

PQZ is a new insecticide product from Nichino America that has been registered since November 2018 but was missed in our earlier updates. PQZ contains pyrifluquinazon as the active ingredient. It is in IRAC group 9B. It controls aphids, whiteflies, and leafhoppers, and is allowed for use on Brassica head and stem vegetables, cucurbits, fruiting vegetables, leaf petiole vegetables, leafy vegetables, tuber and corm vegetables, as well as on pome fruit, stone fruit, and grapes.

Ethos-3D is a new insecticide/fungicide product from FMC that has been registered since 2018 but was missed in our earlier updates. It is for use on sweet corn. It contains bifenthrin (the same AI as in Brigade; IRAC group 3A) as the insecticidal component, and Bacillus amyloliquefaciens as the fungicidal component. It is for application at-planting for control of corn rootworm larvae, Asiatic garden beetle, wireworms, grubs, seedcorn maggot, cutworms, and armyworms.

-Celeste Welty, Extension Entomologist

Using Cover Crops for Weed Control in Spring

Cover Crops are a valuable tool in the toolbox of the backyard grower, community gardener and urban farmer.  I planted a mix of cover crop species last fall in my community garden plot to keep the soil alive over the winter, prevent erosion and increase soil organic matter.

Winter rye, forage radish, hairy vetch and crimson clover blend

This species mix, especially the winter rye component, can be challenging to manage in the spring depending on when the soil is worked.  The winter rye will die from mowing or crimping when it is going to seed and nearing maturity, but when tilled young, some of the grass will continue to grow.

The city tilled the garden in late March, some of the cover crops persisted and will continue to grow without further tillage or herbicide application.

The majority of my plot will be used for summer vegetables.  I do not want to leave the ground bare until that point as the cover crops will continue to grow in spaces and weeds will fill in the rest.  I would also lose organic matter and fertility from spring rains.

I rototilled over half of the plot to create a seed bed about 10 days after initial tillage.  This will kill most of the remaining over-wintered cover crops and created a seed bed for planting.  There is a loss of organic matter from tillage, but I did not have the option to drill in the seed.

I followed up with a planting of Buckwheat.  Buckwheat is a versatile cover crop that tolerates poor soils, rapidly germinates, weed suppresses, attracts pollinators and when mowed, will rapidly break down prior to the next planted crop.

 

 

I will let the Buckwheat grow until mid-May.  Then I will mow the space which will kill both the cover crop and any annual weed that germinates within the Buckwheat planting.  It will also weaken any perennial weed that is growing.  I will let the residue decompose for a few days and then till and apply plasti-culture mulch in the pathways prior to summer vegetable planting.

 

Beware of thrips on strawberries

Although strawberries are not considered to be a vegetable crop, using VegNet is a good way to get information out to growers who have both vegetables and berry crops.

Strawberry fruit that have been injured by thrips are a dull or bronzed color, and are often small, hard, seedy, and fail to ripen. They can cause uneven maturity of fruit. When severe, their injury can make the strawberry crop completely unmarketable.

Thrips are an occasional serious pest of strawberries. This means that in most years, they are not a problem, but in some years, they can be a big problem. One such year was 2018 for some growers in Ohio. As far as we understand the problem, the reason for variability from year to year has to do with weather systems. In some years, conditions are right that large numbers of small insects such as thrips and leafhoppers are carried on strong weather fronts moving from the southern USA into Ohio during the time that strawberries are in bloom. In other years, this long-distance movement does not happen at all, or happens later, at a time when strawberries are no longer in bloom.

Thrips are small, slender, elongate, cigar-shaped insects, about 1 mm (1/25 inch) long. They differ from other insects by having narrow strap-like wings that are fringed with hairs (Figure 1). The wings are usually folded lengthwise over the back when they are resting or feeding (Figure 2). They have asymmetrical mouthparts (Figure 3) that have a well-developed left mandible and an underdeveloped right mandible. They feed by piercing plant cells by the mandible then sucking sap that oozes out of the punctured cells. Thrips generally have flowers as their preferred plant part. They are found in flowers of many species of plants. Thrips are often overlooked due to their small size and their tendency to hide in protected places. When present at low density, thrips are often not harmful to plants.

The thrips species that infests outdoor strawberries is Frankliniella tritici, which has the official common name of ‘flower thrips’, but which is widely known as the eastern flower thrips. It does not tolerate cold weather well so does not survive winter well in places like Ohio. The adults are yellowish brown, and the larvae are whitish-yellow. The larvae are similar to the adults in shape but smaller and without wings. On strawberries, the infestation starts by adult thrips during bloom but then can continue during fruit set by adults and their offspring larvae. Thrips hide under the cap of the berry or in grooves around the seeds on the berry.

A key to thrips management is frequent monitoring, at least once per week. Growers should examine early flower clusters on early cultivars. In each of five to 10 areas of the field, five to 10 blossoms should be tapped into a white cup, or into a zip-top sandwich bag, which should then be examined for the dislodged thrips running around on the surface. Count the number of thrips found, then calculate the average number of thrips per blossom. A rough action threshold for treatment with insecticide is the presence of 2 or more thrips per blossom. Once fruit are ¼ inch in diameter, an action threshold is 0.5 thrips per fruit. If thrips are above threshold, the trickiest part of management is to avoid spraying insecticide that will harm pollinators. Insecticide should be applied pre-bloom or before 10% of the plants have open blossoms. If thrips are found above threshold on early cultivars, then a preventive spray can be made on the later cultivars before their flowers open, to avoid harming pollinators.

Insecticides used to control thrips on conventional strawberries are Radiant, Assail, and Sivanto, all of which have thrips listed as a target pest on their labels. Thrips are well controlled by Lorsban, Brigade, and Danitol, which are allowed for use on strawberries, but thrips are not listed as a target pest of the label of these three products. Note that Lorsban has a 21-day pre-harvest interval. Products for thrips control on organic strawberries are Entrust and azadirachtin products such as Neemix and Aza-Direct.

If a biological control approach is preferred, several kinds of natural enemies are available for purchase from commercial insectaries for thrips control: Orius (predatory flower bugs), and two species of predatory mites: Amblyseius cucumeris and Ambylseius swirskii. Biocontrol is not feasible to begin once the thrips population is large but can be planned in advance at locations that have a consistent problem with thrips.

Figure 1. Typical appearance of a thrips.

Figure 2. A thrips with wings folded over its back.

Figure 3. Close-up of thrips head and mouthparts.

by Celeste Welty, Extension Entomologist