The leaves of balsam pear turn yellow. what's going on?

Balsam pear in the growth period, there will be leaves yellowing, withering, low fruit setting rate and other phenomena, and leaf yellowing is the most common phenomenon, that balsam pear leaves yellowing how to return?

Reason 1. Stagnant water

The root system of balsam pear is more developed, but mainly secondary lateral roots, the regeneration ability is weak, so balsam pear likes wet and is not tolerant to waterlogging. During the growth period, about 85% of the air relative humidity and soil relative humidity are needed, but it is not suitable for stagnant water, which is easy to cause root necrosis, leaf yellow wilt, light affect the result, severe disease and death of the plant.

Solution: after each watering, we should prevent water accumulation in the field for a long time, that is, irrigation is to drain, especially after rain, we should pay attention to timely ditch drainage to prevent water accumulation in the field.

Reason 2. Lack of nitrogen fertilizer

When balsam pear was nitrogen deficient, the leaves were smaller, the upper leaves were smaller, the internodes near the growing point were obviously shortened, the interveins were yellowed, the veins were prominent, and then extended to the whole leaf, with less fruit setting, slow expansion and fruit deformity.

Solution: in view of the lack of fat yellow leaves, we should do a good job in topdressing balsam pear, according to the principle of light in the early stage, heavy in the middle and replenishing in the later stage. Before flowering and fruiting, the plant growth is small, topdressing should be less; after flowering and fruit setting, the amount of fertilizer and water is gradually increased, and in the peak fruiting period, the plant growth and melon bearing are carried out at the same time, and topdressing should be applied again; in the late fruiting stage, the plant begins to senescence, so it should be applied properly to prevent the premature senescence of the plant and affect the fruit growth. After flowering and fruit setting, it is necessary to apply enough fertilizer, 15 kg of urea and 10 kg of potassium sulfate per mu. After the first batch of melons were harvested, about 10 kg of urea was applied each time. In addition, in the sunny evening, foliar spraying 0.2% urea and 0.3% potassium dihydrogen phosphate aqueous solution can promote stem and leaf growth, prolong harvest time, and avoid affecting yield and quality due to plant premature senescence.

Reason 3. Natural aging

Balsam pear has strong branching and luxuriant leaves. In the later stage, due to the lack of nutrition supply, the lower leaves naturally turn yellow and senile.

Solution: balsam pear is mainly based on the main vine, so it needs to be pruned. When binding the vine, remove the side vine below 50 cm of the main vine, leave 1-2 strong side vines above, let them grow, and remove the rest of the side vine in time. Results in the middle and later stage, the senescent yellow leaves in the middle and lower part of the plant and the weak or fruitless lateral branches in the upper part of the plant should be removed as soon as possible.

Cause 4. Anthrax

It mainly occurs in the middle and later stage of balsam pear growth, and it is easy to occur under the condition of low temperature and heavy rain from July to August. Leaf disease, generally from the root of the old leaf gradually upward disease, the disease spot at the beginning of waterlogged round light yellow spots, and then expanded into brown spots, diameter 0.1-0.5 cm, the periphery has a purple halo, sometimes concentric wheel lines, easy to break when dry, serious disease spot synthesis of large patches, leaf dry death, when humidity, leaf disease spots give birth to light gray to reddish brown sticky matter.

Solution: choose 500 times of 70% methyl thiophanate wettable powder Or 80% anthrax Fumet wettable powder, 50% thiram wettable powder, 25% pyrimethrin suspension 1500 times, 68.75% oxazolidone manganese zinc aqueous dispersible granules 1000 times, 60% pyrazolyl carbendazim water dispersible granules 1000 times, 50% pyraclostrobin dry suspension 3000 times, 56% carbendazim chlorothalonil suspension 1500 times, 10 dimethyclozole aqueous dispersible granules 1500 times Spray prevention and control of 3000 times of phenylethyl propiconazole EC, 55-66ml / mu of 20% flusilazole-prochloraz water emulsion, 400,600times of 40% bromobacteria wettable powder and 1000-2000 times of 50% imipramine wettable powder. Spray once every 6-7 days, 3-4 times in a row.

Cause 5. Root knot nematode disease

It was characterized by poor plant growth, dwarfism, yellowing, wilting and necrosis of leaves from bottom to top, no edge or tumor process on the surface of melon, or partly no edge or tumor process, and the plant gradually wilted and withered. However, the disease mainly damaged the roots of balsam pear, the lateral roots and fibrous roots of the damaged plants were more than those of normal plants, and spherical or irregular nodules were formed on the fibrous roots. The tumor is white at first, the texture is soft, and then brown or dark brown, the surface is rough. You can pull out a seriously diseased plant and look at the root to identify it.

Solution: first, 15 days before sowing or transplanting balsam pear, 0.2% hyperosmotic avermectin wettable powder 4-5 kg per mu, or 10% thiazophos granule 2.5-3 kg, fine soil 50 kg mixed to the surface, turned 25 cm deep, and soil disinfection can achieve the effect of controlling nematode damage. Or use 10% parathion granules 3-4 kg per mu, ditch application, or 3% chlorazophos granules 4 kg per mu evenly applied in the planting ditch. At the initial stage of the disease, 1.8% avermectin EC 1000-1200 times, or 50% phoxim EC 1000-1500 times, and other agents can be used to fill the roots. 250-500 ml per plant, once every 7-10 days, a total of 2-3 times.