Causes and Solutions for Yellowing Leaves in Strawberries, Blueberries, Watermelons and Cantaloupes

Strawberries, blueberries, watermelons and cantaloupes are prone to yellowing leaves during their growth. Do you know what causes it? What should you do about it? In fact, middle school biology textbooks already introduce the roles of the various nutrient elements that affect plant growth. Yellowing leaves in green plants are mainly caused by a lack of nutrient elements.

What should you do about yellowing strawberry leaves?

1. Too great a difference between dry and wet: after the plant goes without watering for a long time, the leaves first wilt and then turn yellow; there is also the case where, after a long period without watering, a large amount of water is suddenly given and the plant simply cannot adapt, so the leaves turn yellow.

The right approach: watering strawberries should imitate nature, with sunny days and rainy days (do not water when not dry); remember to water moderately.

2. Changes in ambient temperature: being suddenly moved from a greenhouse to a spot in the airflow of an air conditioner causes yellowing and leaf drop; lack of sunlight affects photosynthesis in strawberries and also reduces leaf transpiration, which disrupts the plant's circulation.

The right approach: place them in a sheltered spot with plenty of sunlight for cultivation.

3. Yellowing and leaf drop caused by a lack of trace elements or by over-fertilization.

The right approach: if light and watering are normal, the yellow leaves are caused by a lack of fertilizer, so apply some fermented rice-washing water or evenly apply 20 granules of compound fertilizer per month under the soil at the edge of the pot.

4. Yellowing and leaf drop caused by metabolism and disease, though it will not cause large-scale leaf drop.

The right approach: if strawberries are planted on a large scale, weeds should first be removed and soil-dwelling pests eliminated. A 1000-fold dilution of 50% phoxim emulsifiable concentrate can be sprayed (wetting the soil layer 5-6 cm deep) to control white grubs, mole crickets and cutworms. If you are growing them yourself, remember to regularly prune dead leaves or use insecticides reasonably.

What should you do about yellowing blueberry leaves?

1. Soil moisture remaining too high for too long causes severe anaerobic respiration in the root system, and ultimately the blueberry's fine roots die, unable to normally deliver water and nutrients to the plant. This blocks chlorophyll synthesis and causes the leaves to turn yellow.

Improvement measures:

(1) Control the amount of watering and keep soil moisture between 18-22%.

(2) Pay attention to drainage during the rainy season, especially in low-lying plots or plots prone to water accumulation. Water accumulation in plots where blueberries are planted must not exceed 24 hours, otherwise the plants may permanently fail to resume normal growth.

2. Poor soil physical structure: the surface tends to crust after watering, or water retention is poor, so that after watering the water cannot penetrate into the soil layer or evaporates quickly. As a result, most roots cannot absorb enough water and nutrients, and the leaves lose water and nutrients, showing yellowing symptoms.

Improvement measures:

(1) Improve the soil and increase organic matter content, preferably between 40-60%. If conditions allow, improve the whole area; to save costs, you can also use the hole-improvement method only.

(2) Replace the soil. The soil for planting blueberries requires a pH of 4.5-5.5, preferably sandy loam. Soil with good aeration and water-holding capacity is favorable for root growth.

(3) Increase organic matter mulch on the surface. Covering the soil surface with organic matter can, on the one hand, reduce water evaporation, and on the other hand, the continuous decomposition of organic matter helps improve the surface soil structure and promotes root growth.

3. Pests and diseases also easily cause yellow leaves, such as damage from aphids and rust disease, and soil-dwelling pests such as white grubs gnawing on the roots, all of which can cause varying degrees of leaf chlorosis.

Improvement measures:

(1) For aphid damage, spray cypermethrin or imidacloprid; for rust disease, spray mancozeb or lime sulfur mixture.

(2) For the soil-dwelling pest white grub, in spring and summer you can apply chlorpyrifos or phoxim granules in holes around the blueberry plant's root zone, or directly drench with liquid emulsifiable concentrate diluted in water.

4. Yellow leaves caused by nutrient deficiency, generally mainly iron-deficiency chlorosis.

Improvement measures:

Apply ferrous sulfate or chelated iron in a certain ratio and at certain intervals, which can improve leaf chlorosis.

What should you do about yellowing watermelon leaves?

1. Yellow leaves caused by improper fertilization

Using undecomposed human and livestock manure, or long-term heavy use of chemical fertilizers, causes too much fertilizer and burns the roots. Some people use excessive poor-quality foliar fertilizer; since many foliar fertilizers on the market contain hormone-like substances, this causes hormone and trace-element poisoning in watermelons, making the leaves rigid, chlorotic, brittle, deformed and yellow.

Control methods: strictly prohibit the use of undecomposed human and livestock manure. Chicken and cattle manure must be fully fermented and decomposed in advance before use. When using chemical fertilizers, it is best to adopt formula fertilization and appropriately increase the application of phosphorus and potassium fertilizers. When applying base fertilizer, nitrogen fertilizer should not be used excessively, to prevent the leaves from turning yellow.

2. Yellow leaves caused by element deficiency

In recent years, because watermelon cultivation has been quite profitable, continuous cropping of watermelons has become prominent, which easily causes element deficiency. The more common cases are potassium deficiency, calcium deficiency and boron deficiency in watermelons, all of which easily cause varying degrees of yellow leaves.

Control methods:

(1) Try not to practice continuous cropping.

(2) For continuously cropped watermelons, while applying nitrogen, phosphorus and potassium fertilizers, add one bag of Guangxing Dibao per mu to condition the soil and activate the various medium and trace elements fixed in the soil, indirectly supplementing the shortage of medium and trace elements. For watermelon seedlings that already show deficiency symptoms, spray 800-fold iodine-boron-potassium solution, which has an obvious effect on preventing watermelon deficiency symptoms.

3. Yellow leaves caused by pest and disease damage

(1) Red spider mite: adult and larval red spider mites gather on the undersides of young tender leaves to pierce and suck the leaf sap. Especially the unopened buds, young leaves and flower buds are the main damage sites, causing watermelon leaves to be damaged and unable to grow normally. Leaves pierced and sucked by red spider mites lose their green color and turn yellow, and in severe cases the leaves can dry up.

Control methods: Remove weeds around the watermelon field (greenhouse) to cut off the source of the pests. Red spider mites have a short life cycle and strong reproductive capacity, so early control should be emphasized. You can spray 1.8% abamectin emulsifiable concentrate at 2000-3000-fold dilution or 2% abamectin at 1500-2000-fold dilution plus 800-fold iodine-boron-potassium solution on the leaves for control.

(2) Downy mildew: Watermelon downy mildew easily occurs in the middle and late stages of watermelon plant growth. This disease mainly harms the leaves. Initially, water-soaked light green small spots appear on the leaves, which then gradually turn yellow. The main cause is that the cultivation site is not well ventilated and inorganic fertilizer application is neglected.

Control methods:

(1) At the early stage of the disease, appropriately control watering; for protected cultivation, pay attention to enhancing ventilation and lowering air humidity.

(2) Cultivate disease-free strong seedlings, increase the application of organic base fertilizer, and pay attention to a reasonable combination of nitrogen, phosphorus and potassium fertilizers.

(3) After harvest, thoroughly remove diseased plants and fallen leaves.

4. Yellow leaves caused by insufficient light

If planting is too dense, ventilation and light penetration are poor, or ventilation in protected cultivation is poor, or watermelons are grown in low-lying land where growth is poor, this can also cause watermelon leaves to turn yellow.

Control methods: while ensuring seedling temperature, open the windows as much as possible for ventilation and air exchange to reduce ammonia gas in the greenhouse.

5. Yellow leaves caused by over-watering

Watermelons are watered differently from other plants, but some farmers do not know this and water once a day; over time the soil becomes too wet, causing severe yellowing of leaves and even root rot. After watermelons enter the flowering and fruiting stage, they are more sensitive to water. If water supply is insufficient during this period, the female flower ovary is smaller and develops poorly.

Control methods: Reasonable watering according to the water requirements of watermelons is the guarantee of early maturity and high yield. Watermelon seedlings need less water, and generally measures to control water and restrain seedling growth are adopted to promote deep rooting and robust growth. During the vine extension stage, water management for watermelons should grasp the principle of combining “promoting and controlling”, keeping the soil alternately dry and wet. After watermelons enter the flowering and fruiting stage. Therefore, during this period it is appropriate to keep the soil moist. The melon-swelling stage is the period when water demand is greater, so watering should be increased to keep the soil relatively moist.

What should you do about yellowing cantaloupe leaves?

1. Drought yellowing

The yellowing from lack of water differs from the yellowing from too much water. The yellowing from lack of water shows as the leaf tips or edges becoming withered and dry, with old leaves turning yellow and dropping from the bottom upward, while new leaves grow relatively normally. Just water thoroughly and adequately.

2. Fertilizer-deficiency yellowing

This shows as the color of tender leaves becoming lighter, appearing yellow or pale green, while old leaves remain relatively normal or gradually turn from green to yellow. Regularly check the potting soil; if it becomes dry and hardened, replace the soil. Usually apply light fertilizer frequently and water with some alum water at the right time to supplement iron.

3. Light-deficiency yellowing

When placed in a shaded environment for a long time, the leaves cannot get enough sunlight and cannot form chlorophyll, so the whole plant's leaves turn yellow and then drop. Supplementing light can prevent this problem.

4. Fertilizer yellowing

Yellowing of flowers caused by too much fertilizer or too high a concentration shows as dry brown tips on new leaves; generally the leaf surface is thick and lacks luster, and is uneven and not smooth, while old leaves turn scorched yellow and drop. Fertilization should be stopped immediately, and in severe cases a large amount of water should be used to flush out part of the fertilizer.

5. Scorch yellowing

When strong direct sunlight hits some shade-loving flowers (such as spider plants and hostas), it easily causes the leaf tips and leaf edges to wither, and yellow patches appear on the sun-facing parts of the leaves. Just move them to a shaded place.

6. Water yellowing

Tender leaves are dull yellow and lack luster, old leaves show no obvious change, branches are thin and yellow-green, and new shoots shrink and stop growing, indicating over-watering. Take the flower out of the pot, place it in a ventilated and cool place to let the soil ball dry naturally, then put it back in the pot.