How to ensure fruit set and control pests and diseases in over-summer watermelon?

Summer is the time when watermelons set fruit and go to market, but excessively high temperatures often affect their fruit-setting rate. The higher the fruit-setting rate, the higher the growers' returns, so everyone is very concerned about this issue. So how do you ensure that over-summer watermelons set fruit? Which pests and diseases need to be controlled?

1. How to ensure that over-summer watermelons set fruit?

1. Fertilizer and water management must be just right

To ensure normal fruit set in watermelon, fertilizer and water management is also very important. Because over-summer watermelon has a short growth period, bio-organic fertilizer can be used as the organic fertilizer, applied at 300-400 kg per mu, along with additional phosphorus and potassium fertilizer. Nitrogen fertilizer should be applied as little as possible; if too much nitrogen fertilizer is applied during the watermelon growing period while phosphorus and potassium fertilizer are insufficient, the plants will grow excessively, making fruit set difficult. The key period for watering is around the flowering time of the watermelon; if the small leaves at the growing tip of the vine curl inward, the leaf color is dull, and the growing tip droops, watering should be done promptly, otherwise flower drop or fruit abortion is likely to occur.

2. Identify fruit-setting ability by flower shape

The ovary of early-maturing watermelon varieties is generally round or oblong, the fruit stalk is thick and long, and the fuzz is sparse; female flowers with larger petals set fruit easily. The ovary of mid-to-late-maturing watermelon varieties is oblong, the fruit stalk is thick and long, and the fuzz is abundant; female flowers with large petals set fruit easily, and the fruit is large with good quality. Conversely, fruit set is not easy.

In summer, temperatures are high, and watermelon is prone to boron deficiency, which leads to flowering without fruit set, so boron fertilizer needs to be sprayed before flowering; Jindie boron can be used at a 1500-2000 times dilution.

3. Identify fruit-setting ability by growth vigor

If the internodes of the watermelon plant become longer, the petioles are slender, the leaves are thin and narrow, the leaf color is light green, and the petiole length is greater than the leaf length, this indicates that vegetative growth is excessive and the plant is growing too vigorously; such plants delay the opening of female flowers and do not set fruit easily. If the plant grows too weakly, the main vine becomes thinner, the leaves become smaller, the petioles are slender and short, the leaves become thinner, and the leaf color is dull; female flowers open earlier, and the ovary becomes smaller and round. Although such plants set fruit easily, abnormal fruit development often results in deformed fruit or fruit abortion.

For excessively vigorous plants, on the premise of taking cooling measures, spray chlormequat at a 1500 times dilution for control; for weak-growing plants, use a combination of spraying and irrigation to promote the transition from weak to vigorous growth. Spraying means foliar application of chitin at a 1500 times dilution; irrigation means applying root-promoting bacterial fertilizer with the water.

2. Which pests and diseases need to be controlled in over-summer watermelon?

1. Watermelon anthracnose

It is mostly spread by seed-borne bacteria. If the plant is infected with the disease in the later stage, the diseased parts produce a large number of conidia, which spread through rain and irrigation and cause secondary infection. Currently, it is the peak period for anthracnose in over-summer open-field watermelon. Actual production shows that in low-lying areas with poor drainage, excessive nitrogen fertilizer application, poor ventilation, and continuous cropping plots, the disease is more severe.

2. Watermelon phytophthora blight

Also called phytophthora rot, commonly known as “dead vines”; it is a soil-borne fungal disease that can occur in watermelon seedlings and adult plants, especially in the later growth stage of watermelon under high temperature and rainy conditions, when the disease develops rapidly and severely. Generally, if the rainy season comes early, rainfall lasts a long time, and the rainfall amount is large, the disease occurs early, the condition is severe, and losses are great. The peak of field disease often follows immediately after the peak of rainfall. The temperature limit for disease occurrence is 5-37°C.

3. Watermelon gummy stem blight

Caused by fungal infection. Large temperature changes, high temperature and high humidity easily accelerate the spread of the disease. In addition, continuous cropping of cucurbits, low-lying terrain, dense crop branches and vines, poor ventilation, high humidity, and weak crop growth all lead to severe disease occurrence.