Fall and Winter Crops are Just Getting Started in High Tunnels

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

As summer crops finish in high tunnels, October and November provides the opportunity to plant a wide range of vegetables for late fall and winter harvest. This is a way to continue providing fresh produce to CSA’s, farmer’s markets, restaurants, schools, and local retail.

Leaf Crops
Options for leafy greens from direct seeding include many mustard family crops such as kale, green and red mustards, arugula, Bok Choi, Napa cabbage, Asian greens such as mizuna, and turnip greens. Many of these greens will overwinter in a tunnel.

Many types of lettuce for cut salad greens and small heads can be direct seeded including leaf types, butterhead-bibb types, romaine, and crisp head types. Lettuce can be grown throughout the fall and winter months.

Beet family greens including beets for greens, swiss chard, and spinach direct seeded in October will provide long term harvests into mid-winter.

Other cool season greens to try as a fall planting in high tunnels include corn salad, cress, and Claytonia.

Newly planted arugula in a high tunnel

Root Crops
Beets, carrots, radishes, and turnips seeded in the high tunnel in October and early November will provide late fall and early winter harvests.

Alliums
Leeks transplanted now for overwintering will allow for late winter and early spring harvest. Green onions (scallions) will produce a fall crop from transplants and will overwinter from direct seeding to produce an early spring crop. Chives and garlic chives seeded in October will produce a crop from late fall through spring.

Other Possibilities
Thick seedings of peas (green shelled or field peas) will provide plentiful pea shoots throughout the late fall and winter.

Herbs such as parsley can be seeded now for late fall through early spring harvest. Cilantro is an excellent choice for fall high tunnel production from direct seeding. There are also several perennial herbs that will produce well from late fall through winter (thyme, oregano, sage, rosemary, mint as examples).

Blister Beetles on Swiss Chard

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

Normally at this time of year when I talk about any insect problems in crucifers I talk about harlequin bugs that feed by sucking out plant juices and inject toxins into the plant. But I have gotten reports about several fields and even high tunnels where blister beetles feeding is defoliating swiss chard (Fig. 1). The presence of blister beetles now is not unusual as they are often found in large clusters in late summer-early fall. They can arrive in large groups, seemingly overnight and can do a great deal of damage in a short period of time.

Adults are large, oblong beetles with relatively large heads, long ‘necks’ and usually with some stripes (but not always) (Fig. 1). Striped blister beetles are shades of gray or brown with yellow stripes running lengthwise on their wing covers. The ash-gray blister beetle is gray, the black blister is completely black, and the margined blister beetle is black with a grayish band around the edge of each wing cover (Fig. 1A). Blister beetle abdomens usually extend past their leathery wings. Striped blister beetles hide beneath plants during the hotter periods of the day, becoming active when temperatures are more suitable for them. If disturbed when on plants beetles will immediately fall to the ground and run. Adults begin laying eggs in late spring or early summer and continue through most of the season. A female can lay one to two hundred eggs just beneath the soil surface and eggs hatch within a couple of weeks.

If you look up blister beetles most of the literature deals with the beetles as a threat to horses and livestock. The beetles secrete and contain within them a blistering agent called cantharidin. Cantharidin is toxic if ingested and it persists in beetles long after they are dead. Humans who ingest the beetle can suffer severe damage to the urinary tract and gastrointestinal lining.

Blister beetles begin feeding on the edges of leaves eventually leaving only stems (Fig. 2). Blister beetles will feed on just about any leaf that grows in a vegetable field such as tomato and other solanaceous vegetables as well as leafy greens, crucifers, spinach and others.

Pyrethroids can be used to control blister beetles on most vegetable crops. Pyrethroids will reduce the damage, but there is often a 7-day pre-harvest interval (phi) with some of the chemicals depending on what the crop is. So be sure to check the label to find the correct phi for the particular product you are using on the particular crop you are using it on. It should be noted that once established, beetles are difficult to eliminate completely. Organic growers have an even more arduous task of managing them. Row covers will keep this pest as well as harlequin bugs off your plants. However, if row covers are not used then I often see diatomaceous earth (DE) recommended for beetle control. If it rains DE does not work very well and overall, I have not had much luck with it controlling the beetles. Spinosad alone or mixed with other products such as neem or kaolin clay have been found to reduce feeding damage in 24-48 hours. Having large numbers of grasshoppers near your vegetable fields over the years can increase blister beetle numbers greatly in the general area.

Figure 1. Margined (A) and Striped (B) blister beetles

Figure 2. Blister beetle feeding resulting in defoliated leaves

Spinach Leafminer and Beet Leafminer

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

In high tunnels and in the field, I have been seeing spinach or beet leaf miner Pegomya hyoscyami and P. betae respectively in swiss chard and spinach. These leafminers are a type of blotch leafminer, creating irregularly shaped mines (Fig.1). Adults are small flies about 1/3 inch in length and gray to brown. Larvae are whitish and cone-shaped. Flies of both species overwinter as pupae in the soil. In April and early May (although this can occur in March if in a high tunnel), flies emerge and lay white eggs in groups of 4-8 on the underside of leaves. Eggs hatch and larvae feed within the leaf tissue. As the larvae feed and develop, they create areas of dead tissue where they have fed. These areas are opaque at first and then later turn brown (Fig. 2). Once inside the leaf tissue larvae are difficult if not impossible to control. The larvae are active for about two to three weeks, before dropping to the ground and pupating in the soil. The entire life cycle is 30-40 days. There are three to four generations per season. Once the summer is over, leafminers will overwinter as a puparium in the soil emerging in early spring the next year to start the cycle again.

Both leafminers feed on spinach, Swiss chard, beets and weeds such as pigweed and lambsquarter. Leafminer activity has little impact on overall plant growth but can be quite damaging to vegetables grown for edible greens. So, a crop such as chard and spinach that you are trying to sell the leaves of are greatly impacted while something such as turnips or beets that you are selling the bulbs of are less impacted (unless you are selling the tops too).

The damage to Swiss chard and spinach I saw probably could have been less if the first infested leaves with leafminers had been removed and destroyed. However, once the population was in its second generation the damage was too extensive. Any additional plantings of spinach or chard this season (or next year) should be planted in a different area of the field because of the pupae still in the soil.

Once the spinach or chard is planted in a new area a row cover could be used to cover the plants and keep the leafminer flies out that eventually will emerge from previously infested areas. Applying insecticides helps prevent adults from laying eggs, but they do not kill larvae that are already feeding within plant leaves. Spinosad (organic) can provide good control and has only a minor impact on natural enemies. Neem oil also can be used to prevent adult egg laying but is not as effective as spinosad. As always thorough coverage is necessary for good control which includes getting the material to the underside of the leaf.

Figure 1. Leafminer in Swiss chard

Figure 2. Leaf mine turning brown

Timings for Late Summer and Fall Harvested Vegetables Revisited

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Plantings for fall harvested vegetables are underway and will continue through August. Timing these plantings can be a challenge, especially where multiple harvests are needed. Plantings from early July through the beginning of September may be made, with cutoff dates depending on the crop, variety, and season extension methods such as row covers, low tunnels, and high tunnels.

These plantings can be divided into 2 groups: 1) warm season vegetables for harvest up to a killing frost and 2) cool season vegetables for extended harvest in the fall.

The three main factors influencing crop growth and performance in the fall are daylength, heat units, and frost or freeze events. A few days difference in planting date in the summer can make a big difference in days to maturity in the fall.

Warm season vegetables for fall harvest include snap beans, squash, and cucumbers. July plantings of sweet corn can also be successful to extend seasons for farm stands. Mid-July plantings of tomatoes and peppers also are made for late harvests, particularly in high tunnels.

Cool season vegetables for fall harvest include cabbage, broccoli, and cauliflower; the cole crop greens, kale and collards; mustard and turnip greens; turnips for roots; spinach; beets; lettuce; leeks; green onions; and radishes.

To extend harvest in the fall, successive plantings are an option. However, days between plantings will need to be compressed. One day difference in early August planting for a crop like beans can mean a difference of several days in harvest date.

Another option to extend harvest in the fall is by planting varieties that have different days to maturity at the same time. This is particularly successful with crops such as broccoli and cabbage where maturity differences of more than 30 days can be found between varieties.

Another way to get later harvests is to use row covers or protecting structures (high tunnels). This can allow for more heat accumulation and will aid with protection against frost and freezes. Decisions on what type or combination of covers/protection to use and when to apply the protection will influence fall vegetable maturation and duration of harvest. In general, plantings of cool season crops can be made 30-45 days later in high tunnels than in outside production.

A final factor for summer planting for fall production is on planting cutoff dates. For example, a crop such as cucumber may produce well with an August 2 planting but poorly with an August 8 planting; broccoli has a wider planting window than cauliflower; turnip greens have a wider planting window than kale.

Planting Window for Fall Harvested Warm Season Vegetables
(harvest September through Frost)

Snap Beans: July 10 through August 10

Lima Beans: June 15 through July 20

Cucumbers: July 10 through August 7 (high tunnel transplanted up to September 1)

Peppers: Transplant up to July 10 (high tunnel up to July 30)

Pumpkins and Winter Squash: Direct seed through June 30, transplant up to July 7

Summer Squash: Direct seed July 15 through August 15 (high tunnel up to September 1)

Sweet Corn: Direct seed July 1 through July 30

Tomatoes: Transplant up to July 10 (high tunnel up to July 30)

Planting Window for Fall Harvested Cool Season Vegetables
(harvest September – December)
For transplants, seed 3-6 weeks prior to desired planting date (8 weeks for leeks and onions).

Beets: Direct seed July 1 through August 10

Swiss Chard: Direct seed July 15 through August 20 (high tunnel up to September 30)

Broccoli: Transplants July 15 – August 20

Brussels Sprouts: Transplants through July 10

Cabbage: Transplants July 1 – August 10

Cauliflower: Transplants July 20 through August 15

Kale: Transplants July 15 through August 30

Kale: Direct seed July 1 through August 15 (high tunnel up to September 30)

Collards: Direct seed July 15 through August 15

Carrots: Direct seed through July 10 (high tunnel up to August 30)

Turnip Greens: August 1 through September 10 (high tunnel up to September 30)

Turnip Roots: August 1 through August 30 (high tunnel up to September 20)

Mustard Greens: August 1 through September 10 (high tunnel up to September 30)

Leeks: Transplant July 20 through August 10

Lettuce (full head stage): Direct seeded August 1 through August 20

Lettuce (full head stage): Transplants August 10 through August 30

Lettuce (baby stage and cut salad mix): Direct seed August 1 through September 15 (high tunnel up to October 15)

Onion (green bunching): Direct seed July 1 through August 30 (high tunnel through September 30)

Parsley: direct seed July 15 through August 15 (high tunnel through September 15)

Radishes (salad): Direct seed August 1 through September 30 (high tunnel through November 30)

Radishes (Daikon): Direct seed August 1 through September 10 (high tunnel up to September 30)

Spinach: Direct seed August 10 through August 30 (high tunnel up to September

Fall Vegetables – Timing Plantings

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Plantings for fall harvested vegetables will be underway in the next few weeks. Timing these plantings can be a challenge, especially where multiple harvests are needed. Plantings from early July through the beginning of September may be made, with cutoff dates depending on the crop, variety, and season extension methods such as row covers, low tunnels, and high tunnels.

These plantings can be divided into 2 groups: 1) warm season vegetables for harvest up to a killing frost and 2) cool season vegetables for extended harvest in the fall.

The three main factors influencing crop growth and performance in the fall are daylength, heat units, and frost or freeze events. A few days difference in planting date in the summer can make a big difference in days to maturity in the fall.

Warm season vegetables for fall harvest include snap beans, squash, and cucumbers. July plantings of sweet corn can also be successful to extend seasons for farm stands. Mid-July plantings of tomatoes and peppers also are made for late harvests, particularly in high tunnels.

Cool season vegetables for fall harvest include cabbage, broccoli, and cauliflower; the cole crop greens, kale and collards; mustard and turnip greens; turnips for roots; spinach; beets; lettuce; leeks; green onions; and radishes.

To extend harvest in the fall, successive plantings are an option. However, days between plantings will need to be compressed. One day difference in early August planting for a crop like beans can mean a difference of several days in harvest date.

Another option to extend harvest in the fall is with planting different maturing varieties at the same time. This is particularly successful with crops such as broccoli and cabbage where maturity differences of more than 30 days can be found between varieties.

Another way to get later harvests is to use row covers or protecting structures (high tunnels). This can allow for more heat accumulation and will aid with protection against frost and freezes. Decisions on what type or combination of covers/protection to use and when to apply the protection will influence fall vegetable maturation and duration of harvest. In general, plantings of cool season crops can be made 30-45 days later in high tunnels than in outside production.

A final factor for summer planting for fall production is on planting cutoff dates. For example, a crop such as cucumber may produce well with an August 2 planting but poorly with an August 8 planting; broccoli has a wider planting window than cauliflower; turnip greens have a wider planting window than kale.

Planting Window for Fall Harvested Warm Season Vegetables
(harvest September through Frost)

Snap Beans: July 10 through August 10

Lima Beans: June 15 through August 15

Cucumbers: July 10 through August 7 (high tunnel transplanted up to September 1)

Peppers: Transplant up to July 10 (high tunnel up to July 30

Pumpkins and Winter Squash: Direct seed through June 30

Summer Squash: Direct seed July 15 through August 15 (high tunnel up to September 1)

Sweet Corn: Direct seed July 1 through July 30

Tomatoes: Transplant July 20 through July 5 (high tunnel up to July 30)

Planting Window for Fall Harvested Cool Season Vegetables
(harvest September – December)
For transplants, seed 3-6 weeks prior to desired planting date (8 weeks for leeks and onions).

Beets: Direct seed July 1 through August 10

Swiss Chard: Direct seed July 15 through August 20 (high tunnel up to September 30)

Broccoli: Transplants July 15 – August 20

Brussels Sprouts: Transplants June 20-July 10

Cabbage: Transplants July 1 – August 10

Cauliflower: Transplants July 20 through August 10

Kale: Transplants July 15 through August 30

Kale: Direct seed July 1 through August 15 (high tunnel up to September 30)

Collards: Direct seed July 15 through August 15

Carrots: June 20 through July 5 (high tunnel up to August 1)

Turnip Greens: August 1 through September 10 (high tunnel up to September 30)

Turnip Roots: August 1 through August 30 (high tunnel up to September 20)

Mustard Greens: August 1 through September 10 (high tunnel up to September 30)

Leeks: Transplant July 20 through August 10

Lettuce (full head stage): Direct seeded August 1 through August 20

Lettuce (full head stage): Transplants August 10 through August 30

Lettuce (baby stage and cut salad mix): Direct seed August 1 through September 15 (high tunnel up to October 15)

Onion (green bunching): Direct seed July 1 through August 30 (high tunnel through September 30)

Parsley: direct seed July 15 through August 15 (high tunnel through September 15)

Pumpkins and Winter Squash: Direct seed through June 30

Radishes (salad): Direct seed August 1 through September 30 (high tunnel through November 30)

Radishes (Daikon): Direct seed August 1 through September 10 (high tunnel up to September 30)

Spinach: Direct seed August 10 through August 30 (high tunnel up to September 30)