Speakers warn of 10 dangers of growing under high tunnels

AFP Correspondent

HERSHEY, Pa. (Feb. 10, 2015) — At this year’s Mid-Atlantic Fruit and Vegetable Convention, Cornell vegetable program Extension associate Judson Reid and Penn State Extension educator Steve Bogash identified 10 pitfalls in high tunnel production, which they say are seldom mentioned in the rush to place a high tunnel on every farm.
Recently, the Natural Resources Conservation Service had offered financial assistance for high tunnels for growers.
But some of these growers who accepted the assistance, Reid said, should not have gone into high tunnel production.
First, the return on investment may not justify the cost.
The input costs of the structure, plastic film and specialized equipment required to effectively produce in a tunnel are higher than field production.
Reid recognized that higher yields and a more advantageous marketing window can offset the higher cost, but in his Extension role he has observed some poorly managed tunnels with less yields than field plantings.
One New York tunnel Reid illustrated realized 17 pounds per tomato plant in the tunnel compared to 32.5 pounds in the field.
There are increased risks, such as metal tube structure and crop failure, in high tunnels. Protected culture growing demands greater attention to detail.
Pest management can be more demanding.
Intense irrigation and fertigation in tunnels serve as ideal conditions for aphids, whiteflies, western flower trips, spider mites and broad mites. Without rainfall, spider mites especially can increase rapidly.
Every crop reacts differently in high tunnels compared to field production.
Irrigation management demands greater care. Reid shared an illustration of tomatoes with blossom end rot, which resulted from calcium deficiency caused by insufficient water. Tunnels require more root zone moisture — growers without adequate water supplies should proceed with caution, Reid said.
Foliar diseases including early blight and septoria leaf spot are typically reduced in tunnels, but brown leaf mold, powdery mildew and botrytis, which occur only occasionally in the field can be rampant in high tunnels.
In fact, one strain of powdery mildew attacks only tomatoes, and the plants in high tunnels are more susceptible.
Viruses spread mechanically, such as tobacco mosaic virus, are more risky because of increased handling of tomatoes such as hand pruning. 
Reid advised buying from reputable seed sources, disinfecting equipment and removing suspect plants immediately.
Also high tunnels have numerous porous surfaces such as straw mulch, soil floors and wood stakes. These conditions are conducive to spores, which perpetuate viruses.
Greenhouses, Reid noted, typically employ more heightened sanitation practices than tunnels.
Because tomatoes are high value and enjoy high market demand, pressure to not rotate crops steadily increases disease pressure with soilborne diseases including fusariums and verticilliums.
In addition, the heavy feeding inherent in tomato production can eventually deplete nutrients, particularly in the root zone, unless carefully managed.
Because high tunnel tomato growers typically strive for season extension, short, cloudy days and clear, cold nights can have negative R values.
Reid said it is possible for the inside temperature, especially in cold spring nights, to be lower than outside.
Under those conditions, Reid said growers usually opt to use low output heaters more than row covers. Both increase production costs.
Time management becomes more critical, increasing more managerial and labor demands for a proactive approach.
Pest populations and infestations tend to develop more quickly, and the space constraints render choices such as canopy management more difficult, yet more essential in tunnels.
Growers frequently face competition from others whose tunnels were subsidized.
Growers who purchased unsubsidized tunnels may have paid 40 to 60 percent more for their first tunnel have higher costs and lower margins.
Reid and Bogash reported that they remain optimistic about the role of high tunnels, but point out they are not ideal for all farms.
Recognizing the less favorable aspects of tunnel production, Reid and Bogash say, balances the favorable programs both have conducted.
Yet, they note that those challenges must be met by growers and carefully weighed before considering high tunnels.