Causes of Acute Seedling Death in Greenhouse Cucumbers and Key Points for Raising Seedlings

Cucumber, a plant of the genus Cucumis in the Cucurbitaceae family. Also known as huanggua or qinggua. The fruit is oily green or emerald green, with soft small spines on the surface. It is widely cultivated throughout China and is now widely grown in temperate and tropical regions. Cucumber likes warmth and cannot tolerate cold, and is one of the main greenhouse products.

Morphological characteristics of cucumber

1. Roots: The root system is not well developed, with the main root mass distributed within the top 25 cm of the root layer. It is aerobic, has weak absorption capacity, and requires loose, fertile soil with sufficient moisture. Its regeneration capacity is poor, so root protection measures must be taken during seedling raising, and the seedling age should be strictly controlled.

2. Stem: Trailing, four-angled or five-angled, hollow, with bristles, indeterminate growth type, easily broken. During the seedling stage the internodes are short and upright; after 5—6 true leaves it begins to elongate and becomes trailing. Tendrils, lateral branches, and male and female flowers are borne in the leaf axils. The length of the stem and its branching capacity depend on the variety and cultivation conditions. Early-maturing varieties have shorter stems and fewer lateral branches, while mid- and late-maturing varieties have longer stems and more lateral branches.

3. Leaves: Cotyledons are oblong-elliptical and opposite. True leaves are palmately shallowly lobed, simple, and alternate, with bristles on both sides. The leaves are large and thin, with high transpiration and high water demand.

4. Flowers: Mostly unisexual flowers, monoecious, axillary. Male flowers appear earlier than female flowers, often several clustered together; female flowers are mostly solitary, with an inferior ovary and parthenocarpic characteristics. Insect-pollinated, cross-pollinated. During rainy seasons or in protected cultivation, artificial pollination can increase yield.

5. Fruit: A pepo, cylindrical to long club-shaped, usually reaching commercial maturity 8—18 days after flowering. Young fruits are green or dark green, with a few being pale yellow or white; the fruit surface is smooth or has ridges, bumps, and spines. From flowering to physiological maturity takes 35—45 d; the fruit is yellow-white or brownish, and some fruit surfaces develop cracks.

6. Seeds: Flat, oblong-elliptical, yellow-white. Each fruit sets 100—300 seeds, with a 1000-seed weight of 20—40 g. Seed lifespan is 4—5 years; in production it is best to use seeds 1—2 years old.

Key points for acute seedling death in greenhouse cucumbers and for raising seedlings

In the process of off-season cucumber cultivation under plastic film-covered greenhouses, when cucumbers enter the flowering and fruiting stage, cucumbers that were growing well previously often suddenly show acute seedling death within a few days. This acute wilt of cucumber develops rapidly and is difficult to control.

Its causes: weather problems, continuous rain or sudden clearing after snow, with temperature inversion leading to rapid seedling death; ventilation problems, when cucumbers enter the flowering and fruiting stage, on sunny days with high temperatures and large ventilation, leaf transpiration is fast, some plants with poor rooting begin to wilt, and those with severe water loss wither entirely; cold damage or freezing damage causing partial damage to the greenhouse film surface, with cold wind invading and causing wilting and seedling death; excessive fertilizer concentration, especially when chemical fertilizer is applied close to the base of the cucumber stem, which can easily burn and kill the seedlings.

In places using greenhouse insulation cultivation, acute wilt of cucumber occurs to varying degrees every year. In order to prevent it early, the following measures should be taken.

1. Water appropriately according to the seedlings and the time.

The cucumber root system is relatively well developed, but new roots mostly form concentrated in the surface soil layer. Avoid watering mistakes that inhibit the proliferation of the root mass, and pay attention to watering according to the seedlings and the time.

Water little at transplanting, and water cautiously for seedling recovery. When temperatures are low, soil moisture is high, or continuous rainy weather occurs, water little or not at all for seedling recovery. When entering the peak fruiting stage, combine topdressing with watering, applying fertilizer with water, about once every 10 days, and strictly prevent a single excessive fertilization from burning the cucumber seedlings. It is best to water in the morning on sunny days, and avoid watering in the afternoon and evening. Do not water the entire greenhouse on rainy days. Water little and often; do not flood-irrigate.

2. Reasonably control the temperature inside the greenhouse.

At the early stage after transplanting, generally do not ventilate. During the day keep the greenhouse at 25°C-30°C, and at night keep it at 12°C-15°C, not lower than 10°C. As the cucumber seedlings grow, regulate air and temperature in time. Its effects include: preventing disease occurrence; avoiding plant aging; supplementing carbon dioxide. However, temperature regulation must be beneficial to cucumber growth. Generally, ventilate when the daytime temperature rises to 30°C, and close the greenhouse film when it drops to 28°C in the afternoon. During the fruiting period, the temperature should not be lower than 12°C.

Regularly clear the ditches around the greenhouse-grown cucumbers to ensure they are unobstructed, so as to facilitate timely irrigation and drainage, and achieve rapid water filtration. Every day check whether the greenhouse film is damaged or improperly covered, and repair it promptly to achieve insulation and warming. Before strong winds and temperature drops arrive, cover with straw mats and secure the ropes to prevent cold wind from invading and damaging the cucumber seedlings.

5 key points for raising cucumber seedlings in greenhouses

First, strengthen seedling-stage management to cultivate strong seedlings and promptly control pests and diseases.

Second, strengthen greenhouse insulation and warming work. When a cold wave comes, pay attention to insulation, and be careful not to water, so as not to lower the soil temperature.

Third, apply less quick-acting chemical fertilizer and more decomposed organic fertilizer, and carry out foliar topdressing. For foliar topdressing, spray leaf fertilizers such as high-efficiency lizhisu and compound potassium dihydrogen phosphate.

Fourth, when it clears after snow, the greenhouse should uncover the straw mats, uncovering while covering, and spray the leaves with warm water at about 20°C, and promptly remove old leaves to reduce transpiration. After the seedlings return to normal growth, all the straw mats can be pulled up during the day. Even on cloudy days, pull up the straw mats as much as possible to let the seedlings see more scattered light, but at night still cover with two layers of protective film, do a good job of insulation, and strictly prevent the seedlings from freezing a second time.

Fifth, water promptly after it clears. Water sufficiently for bottom moisture 15-20 days before cucumber transplanting. If the arable layer is too deep, after watering the bed surface needs to be leveled again, so that the soil reaches the standards of deep, thorough, fine, level, and firm. Note: watering is best done by drip irrigation, avoiding flood irrigation, to maintain good soil permeability.