Key Points of Summer Citrus Pest and Disease Control Techniques

Summer's high temperature and high humidity make it the season with the highest incidence of citrus pests and diseases in the entire year. If pest and disease control is inadequate during this period, it will seriously affect the cultivation of young citrus branches and shoots, affect the development of young fruit on bearing trees, and even trigger massive fruit drop. Therefore, it is essential to effectively strengthen pest and disease control work in summer. According to recent surveys by this station and the Longmen station of citrus orchards in Yangqiao, Longhua, Shajing, Lantian and other partial townships, the current citrus pests and diseases mainly include: anthracnose, canker, foot rot, citrus leafminer, red spider mite, Asian citrus psyllid, longhorn beetle, etc.

I. Pest and Disease Occurrence Situation

1. Anthracnose: Expected to occur at moderate levels, with localized heavy incidence. According to a recent survey by this station in some orchards in Yangqiao, the highest leaf damage rate on nianju (annual tangerine) was 4.6%, with an average of 1.8%.

2. Canker: Expected to occur at moderate-light levels for mandarins and tangerines, and at moderate levels for orange varieties. Among these, the leaf damage rate on Yangqiao orange varieties was 3.6%, the fruit damage rate was 0.7%, and the disease index was 0.12.

3. Foot rot: Expected to occur at moderate levels. The recent increase in rainy days is favorable for the occurrence of this disease. Among these, the highest diseased plant rate in Yangqiao was 2.4%, with an average of 0.5%.

4. Citrus leafminer: Expected to occur at moderate levels, with heavy occurrence in some orchards. Among these, the highest leaf damage rate on Yangqiao citrus was 10%, with an average of 2.4%; in orchards in Longhua, Shajing and other areas, adult citrus leafminers were found on both fruit trees and weeds, with the highest count of 1.3 adults per 100 m2 of weeds (slightly lower than the same period last year), averaging 0.5 adults. The first peak occurrence period is expected to be from mid-May to early June.

5. Red spider mite: Expected to occur at moderate levels. According to a recent survey by the Longmen station in Longhua, Shajing, Lantian and other areas, the highest number of red spider mites per leaf in orchards was 9.3, with an average of 2.6, a decrease of 82.2% compared to the same period last year.

6. Asian citrus psyllid: Expected to occur at moderate levels. Among these, in Yangqiao there were 3 adults and 8 nymphs per hundred shoots. The Asian citrus psyllid is the main insect vector for spreading citrus huanglongbing (HLB), and should be a priority for control. The second peak occurrence period is expected to appear from May to June during the summer shoot germination period.

7. Longhorn beetle: Expected to occur at moderate levels. Among these, in Yangqiao, 3 adults and 8 eggs were found per hundred trees. The longhorn beetle has one generation per year, with the peak egg-laying period from mid-to-late May to early-to-mid June, damaging trees by larval boring.

In addition, aphids, scale insects, whiteflies, inchworms, butterfly larvae, rust mites, scarab beetles, scab, gummosis and other pests and diseases also occur to varying degrees.

II. Control Recommendations

1. Strengthen field management: Bearing citrus trees should undergo timely summer pruning, and young trees should have buds removed and shoots controlled. When more than 70% of the trees in the entire orchard and more than 70% of the shoots on each tree have sprouted, shoots should be released uniformly and pesticide application should be carried out uniformly, which not only helps to concentrate on eliminating various pests and diseases but also greatly saves production costs.

2. Chemical control. All areas should strengthen systematic surveys of citrus pests and diseases, accurately identify the appropriate control timing for major pests and diseases, carry out timely classified control, reasonably mix pesticides, and alternate control agents to slow down pest resistance and reduce pesticide pollution of the environment.

(1) Anthracnose: Options include 80% carbendazim-thiram wettable powder at 800 times dilution, or 50% thiram at 600 times dilution, or 40% sulfur-multi suspension concentrate (Miebingwei) at 300 times dilution, or 80% Bibeike wettable powder at 600 times dilution, or 62.25% Xiansheng wettable powder at 600 times dilution, etc.

(2) Canker: Currently, the main approach is to carry out control when the average fruit transverse diameter is about 2.0 cm, using 0.5% equal-amount Bordeaux mixture, or 77% Kekesha 2000-type at 600 times dilution, or 50% Jiaruinong wettable powder at 600 times dilution, or 30% copper oxychloride at 500 times dilution, etc. In addition, pesticide should be sprayed promptly after each typhoon or heavy rain.

(3) Foot rot: First thoroughly scrape off the diseased areas on the affected plants, then evenly apply 40% sulfur-multi suspension concentrate or ridomil-mancozeb to the diseased areas 2-3 times.

(4) Citrus leafminer: Use 1.8% abamectin at 3000 times dilution, or 20% Kewebao at 2000 times dilution, or 20% Haoniandong at 2000 times dilution, etc., which can also control citrus aphids, Asian citrus psyllids, whiteflies, inchworms, butterfly larvae, etc.

(5) Red and rust spider mites: Regularly inspect for pest activity. When an average of 2-3 red spider mites per leaf is found, or 2-4 rust spider mites on leaves or fruit, or 5-6% of leaves have rust spider mites, promptly spray for control. Use 15% pyridaben at 2000 times dilution, or 50% mandaihzhi emulsifiable concentrate at 1500 times dilution, or 20% mandeishi at 1500 times dilution, etc.

(6) Longhorn beetle: First, for severely affected aged and declining trees, cut them down early to reduce pest sources; second, take advantage of the longhorn beetle's habit of resting at noon to catch and kill adults; third, from June to August, inspect tree trunks and use a small knife to scrape and kill any eggs and young larvae found; fourth, after larvae have bored into the xylem, use a steel wire hook to kill the larvae, or use 80% dichlorvos emulsifiable concentrate or 40% dimethoate emulsifiable concentrate at 5-10 times dilution, soak it into absorbent cotton, and insert it into the boring hole to kill the larvae.