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Growing Organic Cucurbits: Cucumbers to Zucchini

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This article comes from the NOFA/Massachusetts 2013 December Issue Newsletter

Presented by Atina Diffley Reviewed by Adam Dole

At the outset of her talk Atina Diffley steered the audience to the farmer’s resource page of her website, www.atinadiffley.com.  There you can find links to many helpful sites and publications covering all aspects of organic farming. 

She says successful production of organic cucurbits starts with soil building.   To build the depth of loose soil on her farm, 50% of the land is in soil-building cover crops at any one time.   She recommends the following titles to all organic farmers:  Building Soils for Better Crops, Managing Cover Crops Profitably (available free online from SARE), and also SARE’s organic crop rotation guide (also free online). 

Cucurbits are the most sensitive of the vegetables to soil conditions; site selection is critical.  When beginning the season’s crop plan, select the sites for cucurbits first, and put them on lighter land.   The origins of many cucurbit crops are dry regions and even deserts, Diffley explained. Therefore cucurbits thrive in sandy, well-drained soils, not clay.  Also, on her farm they rotate land planted to cucurbits multiple miles apart for pest and disease control.

Pests

Atina advises farmers to understand the life cycles of insect pests in order to effectively control them.  She guided us through her strategic thinking process and shared resources for combating a number of cucurbit pests.

Striped Cucumber Beetle

This insect vectors cucumber wilt and also bacterial wilt.  Adults feed on the leaves of cucurbit plants, spreading disease.  Larvae feed on plant roots. The Striped Cucumber Beetle overwinters in crop/weed debris, bordering vegetation, woodlots, and fence rows.  In order to eliminate overwintering habitat, Diffley recommends clean and thorough deep cultivation, compost application and cover cropping in the fall, to facilitate decomposition of debris where beetles could overwinter.  Rotation is only effective if over a very long distance. 

Since Striped Cucumber Beetles emerge in late April or early May when temperatures reach 55-65 degrees, delaying planting until after June 10th is an effective strategy for control.  Obviously for crops you want to bring to market early, delayed planting is not a good option. In such cases trap cropping is an effective strategy.  Two methods of trap cropping were discussed.  The first involves planting susceptible cucurbits in last year’s cucurbit field, and spraying or burning beetles as they emerge.  Second, surround your primary cucurbits with a susceptible trap variety two weeks prior to your main crops.  Plant multiple rows if pressure is heavy, and be sure to completely surround the main crop plants.  Control beetles in the trapcrop with Pyganic and monitor the pest population.  Row cover can also be used until the threat of Striped Cucumber Beetle has passed.

Aphids

Too much nitrogen attracts aphids, advises Diffley.   Healthy plants with vigorous roots do not require soil-test nutrient levels as high as conventional systems.  Avoiding excess nitrogen application is a first step toward controlling aphids.  Aphids vector hundreds of viruses which they carry on their mouth parts.  Barrier trap crops, such wheat, can alleviate the spread of viruses by cleaning the mouthparts of the aphids.  Applications of non-selective herbicides can increase aphid populations.  Aphids have many natural enemies including lady beetles, lacewings, parasitic wasps, hoverfly larvae, damsel bugs, and soldier beetles.

Squash bugs

The highly toxic saliva from Squash Bugs, which mainly feed on plant foliage, causes the leaves to wilt and entire plants to sometimes die.  The fruits are also fed upon. This pest overwinters as an adult in cucurbit fields, crop debris, and adjacent woodpiles or buildings.   Clean cultivation is a good management strategy. In northern climates Squash bugs produce one generation per year. Squash bugs do have natural enemies such as parasitic wasps.  Diffley recommends piling old squashes in the autumn, which attracts the Squash bugs, and burning the pile to kill overwintering adults.

Vine Borers

This pest overwinters in crop debris in soil to 2 inches deep.  Removal of crop debris and clean cultivation are effective for control.

Diseases

Fusarium Wilt

This fungus can survive in the soil for many years.  It can be spread by wind or on equipment.  The best defenses against Fusarium wilt are using certified disease-free seed, using resistant varieties, and rotating crops out of a particular soil for at least 3 years.  Atina recommends the NC State resistant cultivar list.  Always wash cultivation equipment thoroughly before entering a new field.

Blossom End Rot

This disease is a Ca deficiency in the plant, though not necessarily in the soil.  There may be adequate calcium, but the plant cannot access it.  Roots may not be developed enough. Soil microbes are needed to access soil Ca.

In general, wider plant spacing in the field allows for more air circulation and helps prevent disease.  Atina plants cucurbits 7-9’ between rows.

Transplanting Cucurbits

According to Atina, striped cucumber beetles can smell cucurbits seed germinating, and so planting out transplants can allow your plants to outgrow beetle attacks.  She uses two seeds per cell.  Allowing the plants to become slightly root bound is good.

She uses a low-tunnel laying machine for early cucurbits, including cucumbers.  Having cucumbers before other farmers is a huge economic benefit.  She doubles the size of her first cucumber planting because the demand for the first cukes of the year is extraordinarily high (she makes her most money on the first planting). “Stay in the market,” she advises. “Never break the delivery pattern” to customers.

Pollinators

Pollinators are very important for cucurbits; they require multiple visits for adequate pollination.

Irrigation

Atina uses only drip irrigation on cucurbits.  In general, she does not recommend regular irrigation, unless required to keep the crop alive, until fruiting begins.  Allowing cucurbits to be a bit dry causes the plant to develop vast root systems.  Normally she will not irrigate watermelons unless a large rain is expected following extended dry weather.  A buffer irrigation before the large rain event can preserve melon quality.

Cultivation

Cucurbits have extensive roots systems that extend beyond the area covered by vines.  At 6 weeks old, root systems are well developed, and cultivation deeper than 1” is detrimental.

Harvest, Washing, and Packing

Use of good technologies can save a lot of physically wearing labor.  Harvest washer/conveyors save farmers’ wrists, hands, and backs of farmers.  They are available through Roeter’s Farm Implements.  Also, 3 point hitch forks on the back of the tractor can carry bins which can be filled with melons or squash for delivery to minimize handling of these heavy crops.

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