Integrated Control Methods for Anthracnose in Citrus Cultivation
After damage, it causes leaf spots, fruit drop, and branch dieback, weakening tree vigor and even killing the entire tree, greatly affecting citrus yield and tree vigor. In particular, the rainy and sunless conditions last autumn caused severe waterlogging in some citrus orchards, poor root growth, and weak tree vigor, which allowed the anthracnose pathogen to “take advantage of the weakened trees”, resulting in a relatively large overwintering inoculum base; the strong cold snap in early spring this year also caused freezing damage to trees in some citrus orchards and reduced disease resistance; and the continuous low-temperature and rainy climate since the beginning of spring has been favorable for the massive spread and invasion of the anthracnose pathogen. Therefore, all citrus bases should attach great importance to this and promptly carry out prevention work against citrus anthracnose.
1. Symptoms of anthracnose
When leaves are affected, the lesions often occur at the leaf margins or tips, are nearly round or irregular in shape, slightly sunken, with the lesion margins brown to dark brown and the center grayish brown, scattered or arranged in concentric rings with many small black dots on the surface. When twigs are affected, the lesions are elongated spindle-shaped and slightly sunken. If the lesion extends around the entire twig, the diseased twig dies from top to bottom, turning grayish white, with many small black dots scattered on it, and the leaves on the diseased twig often curl, dry up, and remain attached for a long time without falling. When young fruit are affected, dark green oil-soaked irregular lesions appear at first, then expand to the whole fruit; the lesions become sunken and black, causing heavy fruit drop or mummified fruit that hang on the branches. On mature fruit, the lesions are round, brown, slightly sunken, leathery dry-scab type or brown rot fruit-rot type.
2. Integrated control measures: Strengthening cultivation management, enhancing tree vigor, improving the tree's disease resistance, and applying timely pesticide protection are the key measures for preventing this disease.
1. Eradicate the pathogen source. In combination with spring pruning, prune out diseased, insect-damaged, and dead branches, remove and pick up fallen leaves and fallen fruit, and burn them in a centralized manner. Also, in early March, spray the canopy with 2-3 degrees lime sulfur mixture or 45% crystalline lime sulfur mixture at 300-500 times, or 20% 45 Tongshuai at 2000 times, to thoroughly eradicate the pathogen.
2. Apply pesticide protection at the right time. Spring shoot growth and July-September are the peak periods of citrus anthracnose infection. Early pesticide application for protection can achieve good control effects. For green citrus bases, the following can be used: 2% Junkeduke at 200-300 times, or Daconil M?45 at 1000 times; or 60% Citrus Aonong at 1500 times; or 4% Nongkang 120 at 1000 times; or Zhongshengmycin at 1000 times, applied alternately, for 2?3 consecutive sprays.
3. Scientific management to enhance tree vigor (1) Apply heavy overwintering fertilizer to restore tree vigor in time.
In some citrus orchards in our area that are high-yielding, some citrus growers manage unevenly, and the “on-year and off-year” phenomenon is severe. In an “on-year”, the yield per mu can exceed 10,000 jin, causing severe nutritional “depletion” of the tree, which cannot be replenished in time; the tree vigor becomes too weak and disease resistance is poor. Traditional management habits should be improved, overwintering fertilizer should be emphasized, and it should be applied in a timely and sufficient manner. Fertilization at this stage should account for more than 60% of the total annual fertilizer application, mainly organic fertilizer, with an appropriate amount of quick-acting fertilizer, and should be completed within one week before or after fruit harvest, so as to restore tree vigor and promote flower bud differentiation. This is like nutritional supplementation for a woman after childbirth, conserving strength and restoring vitality.
(2) Deep plowing to improve soil and increase organic fertilizer application.
Most flatland and paddy field citrus orchards in our area neglect deep plowing, have long been excessively applied with N fertilizer, and the soil is severely compacted, with poor “air permeability”, nutrient imbalance, and extreme “leanness”; the tree's disease resistance is poor, and fruit puffiness is severe. Therefore, all citrus bases should plow timely according to soil characteristics, in combination with soil moisture conditions and fertilization timing, and apply heavy organic fertilizer. The specific method is: dig trenches of varying width and 30-40 cm deep outside the drip line of the canopy, and mix well-rotted “composted” barn manure, cake fertilizer, green manure, and other organic fertilizers with N, P, K in proportion and with soil into the trenches.
(3) Scientific pruning to prevent canopy shading.
When citrus orchards are planted too densely, especially orchards with more than 220 trees per mu, the canopies become dense and intertwined after the orchard is established, which favors the breeding and reproduction of pests and diseases and makes control difficult. Therefore, fruit growers in dense orchards should strictly implement the new technique of “light-transmitting pruning, determining yield by pruning”: that is, appropriately thin out relatively crowded scaffold branches to “open skylights”; for orchards with more than 220 trees per mu, distinguish temporary trees from permanent trees and adopt the pruning method of “promoting one and controlling the other, advancing one and retreating the other” to overcome the “on-year and off-year” phenomenon, control yield, and achieve stable and high yield. Generally, for high-yielding citrus orchards more than 7 years old, the yield per mu should be controlled at 3000-3500 kg.
(4) Drain excess water to prevent root hypoxia. According to the climate characteristics of our area with more rainy days in autumn, in the future, paddy field and flatland citrus orchards should especially strengthen the construction of drainage and irrigation channels. Orchards established in paddy fields should be planted on ridges, and flatland citrus orchards should dig 40 cm deep crisscrossing drainage ditches according to the terrain, so as to effectively prevent the harm of “flood irrigation” and “stagnant water” caused by autumn rainy weather.