Growing Early Cucumbers

New Zealand Journal of Agriculture, Volume 96, Issue 3, 15 March 1958, Page 281

Growing Early Cucumbers

By

B. P. COLEMAN

and S. O. GILLARD,

Horticultural Instructors, Department of Agriculture, Auckland

"THE cucumber (Cucumis sativus), a native of Africa and Asia, is undoubtedly the most ■ popular member of the Cucurbitaceae family. The hardier outdoor varieties grow readily in most parts of New Zealand in summer and early autumn, but commercial production of early crops is undertaken mainly in the warmer districts of Auckland Province. The earliest cucumbers are grown in heated glasshouses, but unheated glasshouses, frames, and hotcaps are also used for early crops.

USUALLY production is combined with the growing of other crops, such as pumpkins,' rock melons, tomatoes, and strawberries. Production ranges from 151 b. to 201 b. a plant for glasshouse and cold frame culture and up to 301 b. a plant in the open.

Seed Many growers prefer. to save their own seed and choose vigorous plants carrying heavy, disease-free crops of good shape. Poor-shaped fruits should

be removed from the plant and the selected fruits left to mature thoroughly. In glasshouses it will be necessary to-hand pollinate the female flower. Seed Extraction

Seed extraction is best done by the acid method, 2 fl. oz. of commercial hydrochloric acid being used to each 51b. of fruit. The pulp. should be scooped into wooden or porcelain containers and the acid stirred into the pulp with a wooden stick. Occasional stirrings should ' be given during the next 3 hours, after which the seed may be washed in a fine sieve, under running water before being set out in the sun to dry.

Propagation Plants are raised under glass for setting out in their permanent positions. Seeds are sown in pots of sterilised compost in June for planting in the cucumber-type house and in August for cold frames and outdoors. It is usual to sow 3 seeds in each earthenware pot and allow the strongest plant to remain. The pots are set in large wooden trays Bin. in depth and half filled with sterilised potting mixture. All watering is done to the soil in the trays so that the collars of the plants are kept dry and the risk of

collar-rot diseases reduced. Plants are retained in the pots until the root growth is sufficient to hold the soil together.

Varieties

Of the glasshouse types Telegraph is the main variety grown in heated houses. White Spine and Long Prickly are suitable for unheated houses.

Money Maker and White Spine do well in cold frames and like the Crystal Apple variety are suited for field culture.

Manuring From 4 to 6 weeks before planting the soil should be - manured. An average manure comprises 20 parts of dry poultry manure, 7 parts of bonedust, 5 parts of superphosphate, and 1 part of sulphate of potash applied at 1 ton per acre for outdoor culture and 21b. a sq. yd. for frames and houses. Glasshouse Culture The soil in the house should be sterilised about 4 to 6 weeks before planting takes place in late June. (In the tomato-type house planting should be delayed to mid-September.) In cucumber houses the plants are set out 3ft. apart in single rows along

the centre of the bed and in tomatotype houses they are planted 2ft. apart in rows directly beneath the overhead support wires.

In cucumber houses the plants are allowed to grow until they have six true leaves, when the top is pinched out to induce lateral growths. When the lateral growths have reached about half-way up the wires the tops should be pinched out. To reduce the amount of tying the laterals should be trained between the wires and glass as much as possible. All lateral growth is stopped at a point two leaves beyond the first fruit. Male flowers - should be removed to prevent female flowers being pollin-

ated, which is likely to spoil the shape of the fruits. Older leaves should be cut out to make way for young leaves to develop. Fruit on main stems will not develop good-quality cucumbers and should be removed.

When roots appear on the surface in cucumber houses they should be covered with jin. layer of sterilised soil to which bonedust has been added at 3oz. per sq. yd. The practice is continued as fresh roots appear. Free ventilation is necessary during the day and temperatures should be kept about 70 degrees F. and not ex-

ceeding 75 degrees F. Shading may be necessary from mid-November and the glass can be lightly sprayed on the outside with limewash (lib. of hydrated lime to 20 gallons of water). In the tomato-type houses a very shallow hoeing may be necessary, from time to time to loosen up the soil after consolidation by frequent watering. Watering is best done in the mornings, as this gives the soil time to warm up again before nightfall and avoids any check to plant growth. A good watering once a week is usually sufficient, but the soil should never be allowed to dry out to the stage of causing the plants to flag. During hot weather the plants and floor of the house should be syringed twice daily to maintain humidity.

Cold Frame Culture

The soil and frame should be sterilised 4 to 6 weeks before planting in mid-September. The usual practice is to set plants out evenly in three rows of three in frames 9ft. x 4ft. 6in.

Frames should be set in warm positions and . the beds manured a month before planting. To increase soil temperature the frames and sashes should be set out over the beds as soon as they are manured and prepared for planting.

As the plants grow, the tips of runners should be pinched back to promote lateral growth.

Warmth in the frames should be maintained by careful . manipulation of

the sashes; sufficient ventilation being provided without loss of heat. By the end of November night temperatures are usually sufficiently high to enable the sashes to be removed altogether. The ground should be kept in the same moist condition as for glasshouse culture. Outdoor Culture By the use of hotcaps cucumbers can be produced 6 weeks earlier than those planted in the open without protection. Hotcaps of waxed paper may be purchased made up. Many growers, however, make their own, using a special mould and white waxed paper which is ready cut to size 20in. x 22in. Soil should be prepared and manured 4 or 5 weeks before planting is done about mid-September. A day or two before planting is done shallow drills 6ft. apart should be drawn and blood and bone manure spread along the drills at 11b. to each 2ft. of row and lightly worked in. To promote soil warmth, check weed growth, and also reduce excess moisture from reaching the plants 3ft.-wide black building paper should be laid over and along the drills and the edges buried about 3in. deep to hold the paper in place. At planting, 4in. crossed slits should be cut in the paper at 2ft. intervals over the manured drills and the edges folded under to enable the plant to be set out, after which the paper is unfolded to cover the soil. A hotcap is placed over each plant and held by soil placed round the edge. About 4 weeks from planting a slit should be cut in the top of the hotcaps to allow the plant to grow through. Neither runners nor laterals need be pinched back. The only cultivation work required will be to work up the area between the paper strips and keep weed growth in check.

Disease Control

Cucumbers are subject to several diseases which can cause considerable losses if precautions and control measures are not adopted.

Mosaic Disease

Mosaic disease is caused by a virus. There is a slight yellowing of the veins and crinkling of the young leaves followed by a light and dark green mottle with blistering and distortion and some stunting of the plant. Occasional yellow flecks occur on leaves showing the green mottle and may be a prominent symptom. The fruit is usually free from marking, but may be slightly mottled. Control: As mosaic may be seed transmitted, it is advisable to save seed only from healthy plants. Infected seedlings and plants should be carefully dug up and destroyed, the tools cleaned with disinfectant, and the hands washed with soap and water before handling healthy plants. Aphids which transmit the mosaic may be controlled by fumigating or spraying with nicotine sulphate. HETP at 1 pint in 100 gallons of water or TEPP at -J pint in 100 gallons of water

may be used, but the following precautions should be observed: — 1. Avoid contact of concentrate with skin or mouth; use rubber gloves. 2. Immediately wash off any concentrate accidentally spilt on the skin with soap and running water. Wash after spraying is finished. 3. Keep the material away from the reach of children. 4. Do not eat, drink, or smoke while spraying. 5. Leave the spraying area if inhalation of spray vapour causes headache and tightness of the chest.

Mildew

Cucumbers are subject to two mildew diseases—powdery mildew and

downy mildew. Both are prevalent during warm, humid weather, but the former can also develop under relatively dry conditions. Powdery mildew (Erysiphe cichoracearum): Appears as white powdery spots on the shaded portions of the main stems and on the under surfaces of the older leaves. Later the spots may cover the whole leaf surface. Once established the disease will spread rapidly throughout the crop. Downy mildew (Pseudoperonospora cubensis): Appears as more or less angular, yellowish spots on the leaves, and on the lower surface of these a rather scanty, white, downy growth develops. The individual spots are rarely over Jin. in diameter, but may coalesce, resulting in the death of the whole leaf. Bordeaux mixture 3:4 :50 (31b. of copper sulphate and 41b. of hydrated lime to 50 gallons of water) is effective for the control of both downy and powdery mildew. Applications should be made every 7 to 14 days according to weather and the severity of the diseases. Powdery mildew is the more common of the two and may be controlled by using “Karathane”, which leaves practically no residue on the fruits. “Karathane” may be used as a dusting powder or, as a spray, the wettable powder form may be used at 11b. to 21b. to 100 gallons of water. Applications should be at 7- to 14-day intervals until the mildew is controlled.

Grey mould (Botrytis cinerea) produces a dense, grey, velvety, fungous growth on the stems and tips of the young fruits and may cause severe damage under very humid conditions.

Control: It can be prevented by attention to ventilation and plant hygiene. If infection occurs, however, spraying the plants with 41b. of thiram (50 per cent, wettable, powder) in 100 gallons of water will keep the disease in check.

Sclerotinia disease (Sclerotinia sclerotiorum) : Affected areas on stems become bleached in appearance and infection is followed by wilting of the foliage. If the infected portion of the stem is cut open, hard, black, irregular-shaped bodies will be found lining the hollow portion.

Control: Infected plants should be removed and burnt and the soil sterilised before it is used again for a cucumber crop.

Verticillium wilt (.Verticillium alboatrum): Leaves become yellow from the base of the plant upward and the whole plant wilts. If the stem is cut open longitudinally, the wood is seen to be discoloured brown. Mainly

occurs in spring when temperatures are low. Control: Infected plants should be removed and burnt. Sterilise soil indoors before next crop. Fusarium wilt: Symptoms are similar to verticillium wilt, but disease is mainly troublesome when temperatures are high. Control: Infected plants should be removed together with the soil round the roots. The holes may then be filled with a solution containing loz. of copper sulphate in 2 gallons of water and replanted. Diseased plants should be burnt and soil indoors sterilised before the next crop. Anthracnose (Colletotrichum lagenarium) sometimes causes damping off of cucumber seedlings, but does not usually appear on the plants until they are well established. Pale-green, water-soaked spots form on the leaves. These enlarge rapidly and become reddish brown in the centre, surrounded by a yellowish water-soaked zone. Finally these blotches run together and the leaf dries up and appears scorched. Sunken, elongated, water-soaked areas also appear on the leaf stalks

and stem and may girdle the latter, causing the plant to wilt. Similar pale-green sunken areas are produced near the tips of the fruits; they finally crack and expose the internal tissues, and the fruit becomes yellow and dies off. Control: Adequate ventilation should be given indoor crops and the plants sprayed each week during the early stages of attack with bordeaux mixture 3 : 4 : 50. For field culture, crop rotation and spraying the, plants with bordeaux mixture during the growing period are recommended and if infection is severe, the removal and burning of all plants at the end of the season is necessary. Red spider mite (Tetr any chics bimaculatus): A mite which can scarcely be seen without a lens. In heavy infestations the leaves turn yellow and later die. The tiny yellow to red insects feed on the under sides of the leaves. Control: Spray with HETP or TEPP as for aphids.