Posts Tagged ‘high tunnel’

Season Extension Considerations

Thursday, April 1st, 2010

Gordon Johnson, Extension Fruit & Vegetable Specialist;

Season extension techniques and protected culture have been a hot topic recently, spurred on by the availability of cost share money for high tunnel and hoop house structures. With that in mind, a review of techniques that are available to growers to extend production is in order.

As a starting point, it is important to have clear goals for season extension and crop protection. Goals may include one or more of the following:

● Improving overwintering success
● Providing winter freeze protection and increasing fall through early-spring growth
● Providing frost and freeze protection in the spring
● Obtaining earlier production from overwintering
● Obtaining earlier production from spring plantings
● Extending fall harvest seasons
● Producing in the winter
● Producing year-round
● Producing heat susceptible crops in the summer
● Providing protection from heavy rain
● Providing protection from wind
● Providing protection from wildlife damage such as birds

Soil Modifications
Growers should consider ways to modify soils as the first step in season extension. This includes raising beds or ridges – high beds or ridges have better drainage and heat up more quickly in the spring. With ridges, orienting them so that you can plant on the south side will also provide more spring heating.

Plant Selection and Planting Modifications
A second set of options for season extension involves plant selection and planting modifications. Examples include using transplants in the spring, planting windbreaks between beds, selecting earlier maturing varieties for first spring plantings, using more cold tolerant varieties (or heat tolerant for summer) of current vegetables and fruits that you grow, or changing to more cold tolerant species for early or late production (or more heat tolerant species for summer production). You should also consider shallower planting depth for seeds and planting into in your best drained (or “lightest”) soils for early direct seeding.

Mulch can be used to increase soil temperature, decrease soil temperature, or provide winter insulation. Plastic mulches are used to increase soil temperature and hold heat during night periods. Heating increases of 5-20 F° can be obtained depending on the color of the mulch. Soil heating obtained with different colors from lowest to highest are Black < Red < Blue < Olive or Brown < Clear. White, white on black, and reflective plastic mulch types are used to during summer periods to reduce heat loads. Organic mulch sources such as straw are used for winter protection and insulation of crowns and roots of overwintering plants.

Covers are used to protect against wind, accumulate heat and/or insulate and frost or freeze protect plants. Thin clear plastic row covers with slits, holes, or perforations with wire hoops (or soil ridges) as supports have been used successfully for many years to allow for earlier planting. Thicker plastic (greenhouse film) has also been used as covers but must be pulled on and off to avoid over-heating. Floating row covers and supported row covers including spun bond polypropylene, woven poly, and foam plastic thermal blankets are used extensively for winter protection, for frost and freeze prevention, to increase temperatures, and to increase earliness. The heavier the weight of these materials, the more the protection but light penetration is reduced.

Cold Frames
In years past, considerable production was grown in cold frames, generally large wood sided frames 1-2’ tall, 4’ wide partly buried in the soil with clear covering (glass sash has largely been replaced by rigid plastic or fiberglass for cold frames). This still is a viable system for smaller growers to start transplants, get earlier production and extend fall production, especially of cool season salad greens.

Low Tunnels
As mentioned in the cover section, wire supports with clear perforated plastic can be used as a type of low tunnel to protect plants and increase heating. Larger low tunnels using bows made of metal piping, also known as the “quick hoops” system are also possible. These are essentially miniature greenhouses with reduced air volume. They are covered with one or two layers of polypropylene row covers, clear plastic, or a combination. Low tunnels are used extensively for extended cool season production of leafy crops such as lettuce, spinach, endive, and mustards.

Heat Sinks
Heat sinks are materials that can collect heat during the day and then release that heat over night. Collection devices are usually filled with water and may consist of clear plastic containers or tubes or black plastic containers or tubes. These are placed near plants and when used in conjunction with covers can provide considerable heat buffering.

High Tunnels
High tunnels can be considered an unheated greenhouse with extended upright sidewalls and roll up sides where production is done in-ground (plastic mulched beds are often used for crops like tomatoes). Single high tunnels are usually 48’ or 96’ in length and 14’ to 30’ in width. The extended sides allow for small scale equipment to be used for land preparation and allow for better space utilization. Side curtains are rolled up during warm periods for ventilation and closed to conserve heat during cool periods. When combined row covers over crops being grown inside, additional freeze protection and heat conservation is achieved allowing for extension of production into the early winter and with some crops through the winter.

Larger multi-bay “European” style high tunnels are becoming more popular. These structures may be several hundred feet in length and each bay is 18’-30’ wide (many bays can be added for any width desired). In these multi-bay tunnels is possible to vent bays by sliding the roof cover (so it is more open or closed) as well as by opening sides and ends. They are large enough to allow for machinery to operate for land preparation, mulch laying, and spraying. Crops that can be damaged by heavy rains are often grown in these multi-bay tunnels eliminate injury or defects (such as fruit cracking).

Shade Houses
Extending production of heat sensitive crops in the summertime is done often with the used of shade cloth extended above the crop on a pipe framework. Shade cloth with different shading percentage is available from 30-70%. Black or aluminized reflective shade cloth is available.

For maximum protection, heating, and heat conservation combinations are used. Examples from lowest to highest protection and heating are:

● Plastic mulch + row cover
● Plastic mulch + clear row cover + floating row cover
● Plastic mulch + row cover + heat sink
● Plastic mulch + clear row cover + floating row cover + heat sink
● High tunnel + plastic mulch + row cover
● High tunnel + plastic mulch + clear row cover + floating row cover
● High tunnel + plastic mulch + row cover + heat sink
● High tunnel + plastic mulch + clear row cover + floating row cover + heat sink

Worms in High Tunnel Tomatoes

Friday, September 4th, 2009

Jerry Brust, IPM Vegetable Specialist, University of Maryland;

I have been seeing a great many different caterpillar species in high tunnel tomatoes in the past two weeks and damage is heavy at times (Fig. 1). The worm species consist of yellow striped AW, horn worm, fruit worm, and others. The tomatoes inside my high tunnel have about 23% of the tomatoes damaged due to worm feeding (no controls applied) while outside my high tunnel the tomatoes (same variety as inside HT) have almost no worms in them (no controls applied). My research has pointed toward several causes for this occurrence that I will discuss once all the data is in. Bt products such as XenTari will still work if you apply them weekly and the product is present when small worms feed, but to clean up an infestation of medium to large worms, pyrethroids or Lannate would be best.

 worm damaged tomato fruit

 yellow striped AW on tomato fruit

Figure 1. Damaged tomato fruit from high tunnel and yellow striped AW in tomato fruit

Timber Rot, White Mold or Sclerotinia Rot in High Tunnels

Friday, May 8th, 2009

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

The fungus Sclerotinia sclerotiorum causes disease on hundreds of plant species. Timber rot or Sclerotinia rot is becoming a very serious problem in tomatoes (and other crops) grown in high tunnels. Even when a high tunnel is moved between seasons, the disease can be severe because the fungus overwinters both in and around the tunnels. Usually the primary source of inoculum is outside of a high tunnel. In the spring when the soil is moist, the fungal fruiting bodies emerge and spores (ascospores) are released. These ascospores will be released continually throughout the spring and are carried on wind into the doors or raised sides of nearby high tunnels. Ascospores are usually carried or dispersed less than 330 feet. Therefore it is important to use sanitation within 330 feet of a high tunnel. No plants, leaf clippings, potting mix, or soil from the tunnels should be discarded within this area.

The biocontrol Contans has been effective in managing Sclerotinia diseases in the field. Contans, which is a formulation of the fungus Coniothyrium minitans, parasitizes the survival structures of S. sclerotiorum. If it is sprayed on the area around the high tunnel and watered into the soil, it may help reduce ascospore formation in future years. Because the product is living, it must be handled carefully prior to use. Contans would be a good choice to try in fields or areas around high tunnels, which are used repeatedly for a susceptible crop. See the Contans label for additional information.

Other products labeled for Sclerotinia timber rot are Endura, which is labeled for field use, and Botran, which is labeled for greenhouse use.

The black sclerotia on the small tomato fruit will overwinter and result in ascospore formation in future years. The fruit should be either buried or discarded more that 330 feet from the high tunnel.

 Sclerotinea rot on a small tomato fruit.

Tomato fruit infected with Sclerotinia sclerotiorum.

Greenhouse “Air Pollution” Caused by Ethylene

Friday, April 24th, 2009

Jerry Brust, IPM Vegetable Specialist, University of Maryland;

Ethylene (C2H4) occurs in trace amounts in gasoline and natural gas and is produced when these substances are burned. It also is present in wood and tobacco smoke. Ethylene is a plant hormone produced by plants during their growth and development. However, ethyl­ene produced through defective heating equipment can be detrimental to greenhouse crops, because it is pro­duced in greater quantities. Ethylene pollution influences the activities of plant hormones and growth regulators, which affect developing tissues and normal organ development, many times without causing leaf-tissue damage. Injury to broad-leaf plants occurs as a downward curling of the leaves and shoots (epinasty), followed by a stunting of growth. Other symptoms of excess ethylene exposure include the abscission of flower buds (figure below), petals or leaves; water-soaking of older leaves; chlorosis; and wilting of flowers. Crops vary in their sensitivity and response to ethylene toxicity. The degree to which a crop is affected depends on the variety, temperature, ethylene concentration, and the duration of exposure. High temperatures and high light levels will increase the severity of ethylene damage. In high tunnels that burn propane, kerosene or use motors that burn gasoline and have poor or no ventilation, even minute amounts of this pollutant can cause severe damage to tomatoes. Unvented unit heaters in greenhouses can at times also cause problems. These problems tend to increase in very tight greenhouse structures, i.e., those that have little exchange with the outside air. Symptoms of ethylene damage can be very subtle, especially if there are no plants grown in clean air avail­able for comparison.

Proper heating system installation and maintenance are the best ways to prevent problems. A maintenance plan should include cleaning the unit heater and fuel orifice twice a year. Propane flames should have a small yellow tip when properly adjusted and natural gas flames should be a soft blue with a well-defined inner cone. To ensure proper combustion, heater units should have a clean air intake and should be vented to the outside with a stack, which keeps exhaust gas from being drawn back into the greenhouse through the ventilation system.


Late Season Pests in Pumpkins and High Tunnel Tomatoes

Friday, September 19th, 2008

Jerry Brust, IPM Vegetable Specialist, University of Maryland;

It is that time of the year again; as the season winds down some late season pests can come in and ruin what is left of a dwindling crop. In pumpkins it could be “rind worms” which are any number of caterpillar species that will feed on the outside of a pumpkin and scar the surface or penetrate into the rind. Either way it opens the pumpkin up to secondary infection and causes it to rot much sooner than it should. The other big pest is the squash bug, which will concentrate its numbers and feeding on the pumpkin fruit if the foliage goes down and is no longer there (Fig 1). The nymphs and adults can feed heavily enough that they will “deflate” a pumpkin or reduce its vigor (including the stem) by sucking all its juices out. Any of these pests can be easily controlled with an insecticide application like a pyrethroid; the difficulty is making sure to catch the problem before it becomes too late.


Figure 1. Squash bugs feeding heavily on pumpkin fruit because no vines are left in the field

In high tunnels there has been a surge of worms that have suddenly shown up in the past couple of weeks. As corn and natural hosts of the worm pests begin to shut down the moths are attracted to high tunnel plants that are green and still growing. I have seen hornworms, and yellow striped, beet and southern armyworms in high tunnel tomatoes where they tend to feed on the fruit when they become medium size or larger. Smaller larvae tend to stay on the foliage (Fig 2).



Figure 2. Large worms tend to feed on the fruit while small worms tend to feed on foliage, except for fruit worms, which will feed on the fruit when they are both very small and large larvae. They usually start feeding under the calyx or cap of the tomato as in Fig 3.


Figure 3. Tomato fruit worm feeding under calyx of tomato fruit

Tomato fruit worm, however will attack the fruit when the larvae are very small or large (Fig 3). As with pumpkin pests the tomatoes in high tunnels need to be watched carefully for the next several weeks until we have a frost or two. Bt products will work well as long as worms are small and not attacking the fruit, but other chemicals such as pyrethroids or Avaunt or SpinTor or Lannate will be needed if the worms are large or damaging the fruit.

I am conducting a study looking at tomato production inside a high tunnel (HT) compared with tomatoes just outside the high tunnel with the same number of plants and the same variety all planted on the same day in June. The HT tomatoes have been severely attacked by small and large larvae of several worm species with 40% of the tomatoes being damaged. (I am not treating the tomatoes in order to make the comparison.) However, just outside the high tunnel there have been few worms at all and almost no large worms with only about 5% of the tomatoes being damaged. I am not sure why the worms survive better in the high tunnel-temperatures have not been much different between the HT and outside until the last few days. I will be looking at natural enemies (both insects and disease) and the number of eggs laid by the female moths over the next few weeks to see if there are any differences with these factors.

High Tunnel Tomatoes

Friday, April 25th, 2008

Gordon Johnson, Extension Ag Agent, Kent Co.;

We have more growers that are producing tomatoes in high tunnels. The following are fertilizer recommendations for spring grown high tunnel tomatoes from Penn State University:

Fertility Recommendations – Spring High Tunnel Tomato Crop

Weeks After Transplanting Fertilizer and Amount Applied per 100 Plants in 50 Gallons of Water
1 and 2 Water only, no fertilizer
3 through 6 3 lbs calcium nitrate
7 6 lbs potassium nitrate
8 6 lbs calcium nitrate + 0.25 lbs chelated iron
9 5 lbs potassium nitrate
10 5 lbs 20-20-20
11 5 lbs calcium nitrate + 0.25 lbs chelated iron
12 5 lbs potassium nitrate
13 5 lbs calcium nitrate
14 4 lbs 20-20-20
15 5 lbs calcium nitrate
16 4 lbs potassium nitrate
17 4 lbs potassium nitrate
18 4 lbs 20-20-20
19 3 lbs calcium nitrate
20 3 lbs potassium nitrate
21 3 lbs potassium nitrate
22 2 lbs 20-20-20
23 2 lbs calcium nitrate
24 2 lbs calcium nitrate

Go to for more information.