Posts Tagged ‘vegetable crop management’

Bolting in Spring-Planted Vegetables

Friday, May 20th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Bolting is the term used for flower stalk formation in vegetables. Bolting response may be related to temperature, daylength, or a combination.

Bolting in spinach, lettuce, and some radishes (oriental types) will occur naturally as days get longer. High temperatures will accelerate bolting in spinach and lettuce.

Many mustard family plants need a cold period along with lengthening days to flower. The amount of cold needed depends on the species and variety. Mustards are very prone to cold initiated spring bolting; turnips, Chinese cabbage, and salad radishes require more cold to initiate the bolting response.

In the cole crop group, cabbage planted very early in cold springs may bolt and premature flowering in broccoli, cauliflower, kale, and collards also occurs when planted too early, or if the spring is abnormally cold. However, cole crop transplants have to be of a certain age to be susceptible to this cold-initiated bolting.

Other biennial vegetables such as beets, carrots, and onions also can be induced to bolt but only once plants have reached a certain size (they are past the juvenile growth stage). This is uncommon in our region.

Controlling bolting starts with planting during the recommended planting window. Early planting will contribute to bolting in some crops (such as cabbage), late planting in others (such as lettuce).

Select varieties that are adapted to the spring planting season (an example would be Savannah mustard). Chose slow bolting varieties of spinach and lettuce. Choose spring adapted varieties of oriental radishes and Chinese cabbage.

One issue that complicates this is the use of high tunnels for early production. High tunnels allow for earlier planting but cold snaps still may drop temperatures enough to cause the cold induced flowering response in many of these crops.


No-Till and Strip-Till Fresh Market Vegetables

Friday, April 22nd, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Most fresh market vegetable crops are either grown under conventional tillage or plasticulture systems requiring significant tillage. From a soil health perspective organic matter is the driver for healthy soils and the more the soil is worked, the faster that organic matter is decomposed and lost from soils.

One solution for this dilemma is using no-till, where organic matter can be conserved or increased. The best success story with no-till vegetables has been with pumpkins, which are commonly direct seeded through a killed cover crop mulch (often hairy vetch or rye) or through crop residue (most commonly barley or wheat small grain stubble). The mulch provided keeps pumpkins off of the ground and has greatly reduced fruit diseases and improved quality. Other seeded crops such as sweet corn and snap beans have been successfully no-tilled in the region.

No-till also has been shown to work with transplanted crops. Systems were developed and tested for tomatoes on hairy vetch and for numerous crops transplanted through small grain cover from peppers to cantaloupes. There were several no-till transplanters developed and we tested one at UD back in the 1990s.

Incorporating leguminous cover crops into these systems can reduce nitrogen needs for the vegetable crop being grown. In the pumpkin no-till into hairy vetch system, typically no additional N will be needed.

There are several reasons why no-till has not been more widely adopted for vegetable crops. No-till vegetables cannot be grown for early crops which are often the most profitable, due to soil temperatures remaining cooler, longer. Establishment can be an issue, especially through thick cover crop mulches. Weeds are controlled partially by the mulches and herbicides can be used for residual control; however, weed escapes can be problematic because cultivation is not available as a tool. Certain pests such as slugs, mites, and several insects can be an issue in no-till. Drip irrigation is also more difficult to use in no-till.

An alternative that combines some of the benefits of no-till with conventional tillage is strip-till, where cover is maintained between rows and a 6-12 ft tilled strip is where vegetables are seeded or transplanted. Strips can be formed with narrow rotary cultivators or with strip till coulters. This allows for earlier crops and for better establishment. A subsoiler can be run in the strips to improve root development. Management of the strip area needs to be planned ahead of time so that cover crops do not get too large – strips are formed when cover crops are small. There is also potential to install drip irrigation in the strips. In a strip-till system weed management is critical and residual herbicides will be critical.

Research has shown that for many vegetables, yields in strip till and no-till are comparable or higher than similar season conventional or plasticulture production.

The following are some of the keys to success with no-till fresh market vegetables:

1) Well drained soils are best for no-till and strip-till.

2) Fields to be no-tilled or strip-tilled should have minimal weed seed banks and little or no perennial weed problems.

3) An effective cover crop is required for no-till and strip-till systems to work. The cover crop should produce enough biomass to cover the soil and provide mulch that limits light and weed germination. Winter cover crops that have worked well for vegetable no-till in our area are hairy vetch, crimson clover, rye, vetch-rye combination, ryegrass, and subterrenean clover. For late summer no-till vegetable crops, several of the millets have provided good cover.

4) The cover crop should be easy to kill by chemical or mechanical means and have little or no-regrowth potential. Proper timing of cover crop kill is necessary to avoid reseeding in no-till systems. For strip-till systems, strips need to be formed early in the growth stage of the cover.

5) Attention needs to be paid at planting in no-till systems to provide good soil-seed contact for direct seeding or root placement and firming for transplants.

6) Provision should be made for moving residual herbicides into the soil through the mulch cover. This may require overhead irrigation.

7) Provision should be made to manage weed escapes. This may require spot spraying or hand weeding.


Spring Cover Crops for Vegetable Rotations

Friday, April 8th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

One principle of managing for improved soil health is that you should always have a crop growing on the soil. This will maintain or add organic matter, provide benefits from the action of growing roots, and recycle nutrients.

Where fall cover crops were not planted due to late harvest, spring cover crops can be planted and provide some benefit where vegetables are not scheduled until late May or June. Cover crop options for early April planting include spring oats, mustards, and annual ryegrass. Plant oats at 90-120 lbs per acre, mustards at 10-20 lbs per acre, and annual ryegrass at 20-30 lbs per acre if drilled. Increase seeding rates by at least 50% if surface broadcast. These cover crops can be no-tilled into soybean or corn stubble.

Managing Windbreaks in Vegetables

Friday, April 8th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Many vegetable growers plant windbreaks between areas where plastic mulch will be laid and vegetables will be transplanted. Windbreaks are often planted between every bed, every 2 or 3 beds, or in drive rows between groups of beds (4-8 beds). Windbreaks protect young transplants from wind damage and blowing sand and can help maintain higher bed temperatures by reducing heat losses from cold winds blowing over beds.

Most commonly rye is used because it is early and is tall compared to other small grains such as wheat or barley. There are several considerations when managing these rye windbreaks. In most cases the rye should be killed with a herbicide, most commonly paraquat, after it has reached full height. This is when the seed head has emerged. Consideration should be given to reduce the chance of seed formation which can become a weed issue in following crops (especially fall planted wheat or barley). When rye produces seed heads, and those seed heads begin to flower (pollen bearing anthers emerge from the seed head) and pollinate, there is about a 7-10 day period before viable seed is formed (seed is set). Burndown should occur before seed set.

If the field is to be followed with cover crop where there is no concern about the rye germinating in the field, then it can be allowed to go to maturity (normal between bed herbicide applications with shielded sprayers may still kill the rye before it reaches full maturity).

One issue with windbreaks is the movement of mites and insects out of the rye and onto the crop after it dies from burndown with a herbicide. Growers should be aware of this issue and plan for control measures during this burndown period if crops have already been planted. If windbreaks are allowed to mature naturally, this rapid outmovement of pests may be reduced initially but may be extended over a longer period.

For very early transplanted vegetables (April-early May) where rye windbreaks are between every 1-3 beds, the rye often is still elongating and may not have produce a seed head. In this situation, vegetables are transplanted before the rye is killed. The rye is managed with row middle herbicide treatments scheduled before vines start to run off of the plastic for vining crops such as watermelon or before staking for upright crops such as tomatoes. A shielded row middle sprayer is used and paraquat is added along with residual herbicide treatments.

For vegetables to be planted after rye has reached full height (May plantings), then a broadcast burndown with paraquat applied over plastic beds and windbreaks is often used. Transplating is delayed until a rain or irrigation has washed off the plastic. Do not use glyphosate for this type of burndown over plastic due the the potential for residuals washing into planting holes, affecting transplants

Where windbreaks are only in drive rows, then they should be killed before seed has set.

Fordhook Lima Bean Production

Friday, March 11th, 2011

Emmalea Ernest, Extension Associate – Vegetable Crops; and Gordon Johnson, Extension Vegetable & Fruit Specialist;

The original Fordhook lima bean was collected by Harry Fish in 1904 in Carpinteria, California. Carpinteria is a coastal town located just north of the Oxnard Plain. The Oxnard Plain, being surrounded by mountains on three sides and the Pacific Ocean on the fourth, enjoys a moderated climate with highs between 65 and 75°F and lows from 45 and 60°F year round. The Oxnard Plain continues to be the premier location for Fordhook lima bean production and yields can be upwards of 4 T/A.

Fordhook limas were introduced to the US at large by W. Atlee Burpee & Co. in the early 1900s and their popularity soon led to production for processing on the East Coast, particularly in New Jersey and Delaware. Yields of Fordhooks have historically been lower on the East Coast, probably because they are not as well adapted to the climate, and from early on, were plagued by downy mildew caused by Phytophthora phaseoli. Renewed interest in Fordhook production in Delaware has prompted us to produce this summary of recommended practices for Fordhook production, based on research done in the region.

The two Fordhook varieties that are available at the present time are Concentrated Fordhook (CFH) and Fordhook 242 (FH 242). Both are selections from the original Fordhook variety and have white seed. The USDA lima breeding program released a number of green seeded varieties with downy mildew resistance in the 1970s and 80s (F 1072, F 169, F 90-1), however none of these varieties are commercially available any more.

Results from Fordhook yield trials conducted over four decades at the UD Research and Education Center in Georgetown, DE are summarized in Table 1. This data represents 22 separate trials of Fordhook varieties. The average yield over all of the trials is 2521 lbs shelled beans/A. Because some trials included very poorly performing experimental varieties, this average yield is somewhat lower that what would be expected with commercial varieties. The average yield for FH 242 in the trials (7 years) was 3703 lbs/A and the average yield for CFH in the trials (3 years) was 2908 lbs/A.

Table 1. Summary of Fordhook Lima Bean Variety Trial Results 1972-2010 Including Planting Date, Days to Harvest, Yield of Shelled Beans in Lbs/A, Number of Lines Tested and Description of Trial Entries.

Year Planting Date DTH Yield


# Lines Tested Description of Trial Entries
2010 28-Jun 98 3628 1 CFH
2009 11-Jun 97 1234 1 CFH
2008 13-Jun 94 3863 1 CFH
2002 13-Jun 89 1909 2 F 90-1 + breeding lines
2000 12-Jun 93 1525 7 1072 + breeding lines
1997 25-Jun 93 3267 4 F 1072 + breeding lines
1996 26-Jun 85 1584 5 F 1072 + breeding lines
1995 21-Jun 93 4152 7 F 1072, F 90-1 + breeding lines
1994 1-Jun 101 1429 6 F 1072, F 90-1 + breeding lines
1993 18-Jun ? 1480 4 F 90-1 + breeding lines
1992 27-May 140 1282 4 F 1072 + breeding lines
1991 28-Jun 115 2393 3 F 1072 + breeding lines
1990 5-Jun 92 1882 1 F 1072
1989 23-Jun 90 1747 3 F 1072 + breeding lines
1987 ? ? 2853 8 F 1072 + breeding lines
1984 4-Jun 78 1079 4 FH 242, F 1072 + breeding lines
1979 5-Jul 88 4651 10 FH 242, F 169, + breeding lines
1976 7-Jul 86 3742 2 FH 242, F 169
1975 2-Jul 94 2289 4 FH 242, F 169, F 1072 + breeding lines
1974 10-Jun 73 3612 6 FH 242, F 169, F 1072 + breeding lines
1973 6-Jun 77 4177 4 FH 242, F 169 + breeding lines
1972 26-May ? 1686 4 FH 242, F 169 + breeding lines
Overall Average 93 2521

One oft-aired complaint about Fordhook lima beans is that they yield inconsistently in Delaware. The range of yields reported in the above table, 1079-4177 lbs/A, would seem to attest to this. There are however, some management practices that can be used to reduce the potential for yield variability.

Sites and Soils
Historically, much of the Fordhook lima bean production in the region has been done close to the coast (Delaware Bay, Atlantic Ocean) because of the moderating effect of the water on temperature. Inland sites will have greater temperature fluctuations and as a result more variable yields. Coastal sites also have heavy dews, fogs, and higher humidity that will improve pod set. However, this can create an environment favorable for downy mildew. Fordhooks will grow well on a range of soil types from loamy sands to silt loams but require good drainage. Higher moisture holding capacity soils such as silt loams or those with high organic matter content will provide for better performance.

Planting Date
Fordhook lima beans are more heat sensitive than baby limas. They should be planted at the end of June or very beginning of July so that they are not exposed to high temperatures during flowering. They can also not be planted as late in the season as baby limas, because they require, on average, 93 days to harvest, versus the 75-85 days required by baby limas. Based on the trials summarized above, the average yield for trials planted before June 20 was 2096 lbs/A, while the average yield of those planted after June 20 was 3050 lbs/A – a difference of almost 1000 lbs. Risk of split sets or delayed sets is higher with early plantings. This narrow ideal planting window often leads to a narrow harvest window which can affect plant scheduling with high volumes in a short period of time.

Stand Establishment
Fordhook lima bean seeds are large and rough handling before or during planting can cause reduced viability and stand loss. Set up planters to limit bounce in seed drop and plant at slower speeds. Ensure good soil to seed contact with proper press wheel adjustment. Plant at a 1 ½ inch depth. Soil crusting during emergence can also have a devastating effect if the cotyledons are trapped in the soil and the hypocotyl breaks in half. The resulting “headless” seedlings will not recover. Similarly, if only one of the two cotyledons emerges intact, the plant will be stunted. The large seeds are also susceptible to attack by insects and pathogens. Use high quality, treated seed and handle it gently. Make sure soil conditions are optimal for germination and emergence in terms of moisture (temperature should not be an issue in the ideal planting window) so that seedlings emerge quickly and are not exposed to excessive insect and disease pressure. Be prepared to irrigate to maximize germination and to limit the effect of crusting. Lima beans compensate well for stand loss, however, the resulting larger plants will be slower to mature and are more difficult to harvest mechanically.

Fordhook lima beans should not be grown without irrigation. Adequate irrigation can mitigate stress induced by heat. Peak water usage will be from flowering through early pod set where plants will be using from 0.25 to 0.33 inches of water a day.

Fertilizing Fordhook lima beans will be similar to baby lima beans. However, because of the longer season, the higher Nitrogen (N) rate should be used, especially on sandier soils. Apply 40 lbs of N preplant or at planting and follow with a sidedressing at final cultivation of an additional 40 lbs of N. This will be 80 lbs of total N. When following peas, 20-30 lbs of total N will be adequate. Phosphorus (P) and potassium (K) requirements are the same as for baby lima beans. See the Delaware Commercial Vegetable Production Recommendations for specific P and K recommendations according to soil test levels.

Diseases and Insects
Neither FH 242 nor CFH have resistance to downy mildew. Late June and early July planting dates mean that Fordhooks will be setting pods during the cooler part of the season when downy mildew and white mold are most problematic. Effective controls are available for both of these diseases in lima bean and should be employed if necessary.

Also be aware that Fordhook limas maturing in the fall will also have more exposure to worm pests that attack pods. Stinkbugs and Lygus bugs are another concern for pod and seed damage. The large pods are very attractive to these pests at a young stage.

See the Delaware Commercial Vegetable Production Recommendations for specific guidance on lima bean disease and insect management.

Because of the large seed, pod and seed loss at harvest will have a large effect on crop recovery and yield. All efforts should be made to reduce harvest losses. This includes making sure fields are as level as possible, there is limited ridging from cultivation, and harvesters are operated to maximize recovery.

Crop Rotation Planning and Revision

Friday, September 17th, 2010

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Fall is a good time for vegetable growers to plan or revise rotations. The following are some general thoughts on rotations.

Three years is the minimum rotation for crops in the same family or with similar disease profiles. Five or more years is recommended for vine crops. Field crops such as corn, small grains, and sorghum are good rotational crops. Soybeans may be a good rotation for some crops but not for legumes such as lima beans or snap beans.

Problems often arise where growers increase vegetable acreage without adequate ground for rotation. Base your acreage decisions on available fields that fit rotational schemes.

Where vegetables are the main income for a farm, consider using soil improving crops (green manures, biofumgant crops, soil improving cover crops) in lieu of standard field crop rotations. While some income will be lost on field crop revenues, there will be long term gains with improved vegetable yields.

Where rotations are tight, it is critical to consider some disease reducing crops in the rotation (mustard family and sorghums for example). Try to build up organic matter in these fields as this generally improves overall soil health.

Rotate vegetable families where possible. Do not rotate within a family (such as the bean family, vine crop family, or tomato family). Sweet corn is an example of a good vegetable rotational crop to break up disease cycles on many farms.

Vegetable Disease Updates – September 17, 2010

Friday, September 17th, 2010

Bob Mulrooney, Extension Plant Pathologist;

Nematodes in Veggies
Fall is the best time to soil sample for nematode pests such as root knot, lesion, and other plant parasitic nematodes. After fall harvest but before any fall tillage is done, take soil cores six inches deep between plants in the row. Samples should be taken in the root zone of the old crop. Twenty cores/ sample should be taken from random spots in the field and placed in a plastic bucket, gently mixed, and a pint of soil submitted for analysis. Large fields should be subdivided into blocks of 15- 20 acres each and sampled separately. Nematode test bags and instructions are available for purchase from the county Extension offices. Samples cost $10.00. Fall sampling for root knot nematodes is strongly recommended for fields that will be planted in cucumbers, watermelons, cantaloupes, lima beans or other high value vegetables where root knot could reduce production. Forms and instructions are also available on the web at Just a reminder, as I mentioned last week, do not take nematode samples until we get some rainfall if the soil is very dry.

Fall sanitation
In vegetable production it is not a good idea to leave old crop residue in the field any longer than necessary. If the crop is allowed to survive after harvest, fungi that cause many diseases continue to increase on the surviving plants. This allows higher numbers of the fungi to potentially survive until next season. Sanitation (plowing or disking the old crop) will help prevent pathogen carry-over.

Lima Beans
To date, I have not heard about or seen any samples of downy mildew in lima beans. The weather has not been favorable for infection.

September Vegetable Observations

Friday, September 10th, 2010

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Lima Beans
Lima bean harvest is fully underway across the region and the following are some observations in this challenging year. Late May, June, and some early July plantings lost the first set almost completely (heat induced blossom and small pod abortions). The second set is extremely variable and in many fields, economic yields will depend on what happens with the third set. Growers have commented that they are letting fields advance well above the 10% white/dry seed level that is normal for harvest to allow the later set to fill. Some fields are being harvested at the 20-30% dry seed stage (coming from the earlier set). For harvest considerations, it is better to lose a set completely and harvest the later set than to have a bad split set.

There is still considerable dry land lima bean acreage and I am always amazed at how much drought that lima beans can stand without wilting or showing outward water stress. Plants may be smaller but they survive drought and heat very well. Unfortunately, even though lima beans can survive drought, pod set will be limited. Research has shown over and over again that irrigation is necessary to achieve high lima bean yields. In a year such as 2010 where excess heat is also an issue, pod set can be adversely affected, even under irrigation.

We should emphasize again that water is still the most important nutrient for high lima bean yields. In a research plot area where we were looking at residual effects of biofumigant crops and compost this year, we planted snap beans and lima beans in early June as test crops in a dry land situation. After several weeks of drought and heat the snap beans were wilting during the day and were stunted while the lima beans kept on going. To rescue the plots (so that we could get data), we installed drip irrigation between every 2 rows. The snap beans did recover somewhat but with permanently stunted plants, poor bean quality, and a severe split set. In contrast, the lima beans lost the first set but did put on a decent second set and had good plant health and plant size.

Snap Beans
Summer planted snap beans for September harvest are yielding much better than the summer harvested crops. We are seeing yields in the normal 4 ton/A or better range where there was adequate irrigation (compared to summer yields in the 1-2 ton range).

Pickle Cucumbers
Late crops of pickle cucumbers are variable, largely due to stand loss and inadequate water in fields planted during summer high heat periods. In addition, downy mildew has hit a number of later fields adversely, even where fungicides were applied in a timely manner. Pickle harvest should be completed in the next 7-10 days.

I am amazed at how long some watermelon fields have produced this year where attention has been paid to vine health, nutrition, and water. This certainly is the year where you are able to evaluate the yield potential and longevity of main season varieties and effectiveness of pollenizers. On another note, watermelon fields with good weed control (morningglory in particular), had much better later yields.

Tomatoes had a difficult year in 2010 with most fields having much shorter harvest periods due to the extra heat stress. This is especially evident where beds were allowed to dry out at any time during these stressful periods. Somewhat surprising also is the presence of more disease than would be expected in a dry year.

Late Summer and Early Fall Consideration for Vegetable Growers

Friday, August 20th, 2010

Gordon Johnson, Extension Vegetable & Fruit Specialist;

While there will still be hot days ahead, late summer and early fall bring different challenges and opportunities for vegetable growers. The following are some considerations at this time of year:

● The day length is getting shorter each day and there is less heat accumulated during the day. We have passed the latest planting dates for most summer planted – fall harvested crops to go to successful harvest. A good example is with cucumbers where a 2-3 day planting difference in early August (between August 7 and August 10 for example) will mean the difference between a successful crop and a crop that will not mature in time or that will have low yields. Remember that you are up against the first frosts with many of these crops. There is still time however for many of our frost tolerant crops. Greens, earlier maturing broccoli, spinach, and lettuce for harvest in leaf stage can all be planted through the end of the month for fall harvest.

● Extending harvest seasons is a consideration, especially for smaller growers who sell directly. Floating row covers, low tunnels, and high tunnels are all tools to use for frost protecting sensitive crops (such as a late crop of tomatoes) and for carrying cold season crops into the winter and sometimes over the winter. Older methods such as field storing root crops (think parsnips, turnips, carrots) using mulches for later digging can still be employed.

● Late summer and fall planted overwintering crops will be planted over the next 2 months. This includes plasticulture strawberries, spinach, and garlic. However, there are many other vegetable crops that can be successfully overwintered, especially vegetables in the mustard family and onion family and even some cold hardy legumes.

● Cooler nights and lower duration of high temperatures during the day helps to maintain pod set on snap bean and lima bean crops that will be harvested in September through mid-October. This year has been particularly hard on bean crops maturing in July and August.

● Irrigation management becomes less of a challenge for fall crops because evapotranspiration is reduced. Attention should be paid so as not to over-irrigate as the late season progresses to avoid disease problems.

● Late summer and early autumn brings new challenges in regards to pests. This is the time of the year when we see peaks of many insect pests (such as corn earworm), migratory insect populations that have arrived or will arrive in high numbers, and late season insects in higher numbers. With the lower temperatures and longer nights, dews are heavier, often leading to increased disease pressure and the appearance of late season diseases. Throw in a hurricane or tropical storm during this period it can be a recipe for disaster in some vegetable crops.

● This is also the time of year when growers should be planting cover crops, windbreaks, overwintering biofumigant crops, and overwintering legumes for nitrogen sources where next year’s vegetables will be planted. For a review of these options see the WCU article titled Late Summer and Fall Cover Crops for Vegetable Ground in WCU 17:24. Good rotations are critical for vegetable crop production and planning should start now.

And the Heat Goes On

Friday, August 13th, 2010

Gordon Johnson, Extension Vegetable & Fruit Specialist;

In June we had 12 days with temperatures in the 90s, in July so far we have had 15 days with high temperatures 90°F or higher with 2 of those days at or over 100. What has this meant for vegetable crops in Delaware? First, yields are off in most crops from snap beans to sweet corn. The processing snap bean crop is one of the worst we have had in many years with low tonnage and split sets. Watermelon yields are variable with later planted fields with no middle set (crown and late, not much between). Most vegetable crops are at least 7 days earlier than normal with some running as much as 2 weeks early. We are likely to have a shortage of watermelons in late August and for the Labor Day market. Cantaloupe plantings are coming off early and together. And we have August to come – we need lower temperatures for our lima beans and other fall harvest crops to yield well.