Causes of Cotton Blindness and Control Measures
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In recent years, the occurrence of damage to cotton cocoons has been on the rise due to factors such as crop layout, climate conditions, and field management practices. The mortality rate of infected cotton plants typically ranges from 30% to 40%, with up to 60% to 80% of the crops suffering from damage. This can lead to a reduction in yield by 10% to 20%, and in severe cases, as high as 50%. Below are the characteristics, causes, and comprehensive measures for prevention and control.
First, the nature of the damage:
The adult cotton aphids and nymphs feed on the sap of cotton plants, causing symptoms such as leaf drop, broken heads, and clumped foliage. During different growth stages, the damage manifests differently. In the cotyledon stage, the growing point is damaged, turning black and dry. After true leaves appear, the top bud is affected, leading to the growth of adventitious buds, resulting in "multiple cotton" phenomena. When young leaves are attacked, small black spots appear. Once the leaves unfold, they break off in large numbers, known as "broken leaf madness." Young larvae and buds are also targeted, initially showing yellow-brown spots that eventually dry out.
In addition to cotton, these pests also affect beans, legumes, vegetables, and fruit trees.
Second, the morphological features:
The cotton aphid belongs to the order Hemiptera and is commonly referred to as a blind bug. Green-blind nymphs, blind fleas, and three-point blind plagues have been the primary culprits of cotton damage in Xinle City. Adult aphids are approximately 5 mm long, with green forewings and dark gray membranous parts. Their bodies are green, and they have strong flying abilities. Eggs are elongated and yellow-green, measuring about 1 mm in length and 0.26 mm in width. Newly hatched nymphs are green and go through five instars before becoming bright green adults.
Third, the occurrence patterns:
Green-blind crickets produce five generations per year in our city, with two to three generations affecting cotton. The life cycle of L. lucorum is long, with nymphs taking 12–30 days and adults 37–56 days. Overlapping generations are common. Wintering eggs are found in quails, wild Artemisia, pomegranates, fruit trees, and dead cotton branches and bolls. They begin to hatch in early April of the following year. Adults emerge between mid-April and early May, primarily feeding on grasses and other host plants. By mid to late June, they invade cotton fields, reaching peak infestation in late June and July, causing significant leaf and bud loss. By mid-August, they move back to winter hosts and remain there until early October, when they start laying eggs for the next season.
L. lucidula thrives in densely planted cotton fields, preferring temperatures between 20°C and 30°C, with humidity around 80%, which supports egg hatching and pest development.
Fourth, the reasons for increased infestations:
1. Increased availability of host plants: With agricultural restructuring, the number of crops like alfalfa, beans, cotton, vegetables, and fruit trees has grown, providing more food sources and increasing the pest population.
2. Favorable weather: More rainfall in June and July creates high humidity, which is ideal for insect development.
3. Crop conditions: Excessive rain and poor field management, such as inadequate pruning and chemical control, lead to excessive plant growth, inefficient flower buds, and high nitrogen levels, all of which favor aphid breeding.
4. Lack of awareness among farmers: Many cotton growers lack proper knowledge, delaying treatment and missing critical control periods.
Fifth, integrated prevention and control measures:
1. Agricultural control: Remove weeds before wintering eggs hatch to reduce pest populations. Apply fertilizers rationally to avoid overgrowth. Prune damaged cotton plants, especially long shoots, and remove weak branches to maintain 1–2 main stems.
2. Chemical control: Based on the behavior of the aphids, implement uniform spraying across adjacent fields to prevent migration and improve control effectiveness. Monitor regularly and take action when the damage rate reaches 5% or spotted plants are observed. Timely intervention during mid-June to mid-July is crucial, with treatments every 5–7 days, sometimes up to 3–4 times. Pay special attention to fast-growing, dense cotton fields. Spray best before 9:00 AM or after 5:00 PM. Recommended chemicals include a mix of organophosphate and pyrethroid pesticides diluted at 1000 times. Alternatively, use 5–10 grams of 10% imidacloprid and 25–30 ml of pyrethroid per barrel, or 3,000 times diluted 2% methyl azithromycin for effective control.