Can T20 eradicate citrus red mites? Let the facts speak for themselves.

 

 

 

With the growing popularity of heavy-lift agricultural drones such as the AGRAS T16 and advancing spraying technology in recent years, more and more orchards in southern China have gradually replaced traditional manual spraying methods with efficient crop protection solutions.

 

However, pest control for fruit trees is more complicated and challenging than for field crops, especially against red mites on the back of leaves. For many farmers who haven’t used the AGRAS T16, protecting crops using drones remains a big question.

 

 

 

Red mites

 

Let's dive into the evident to find out if drones are truly an effective solution against the citrus red mites. In July 2019, a red mite infestation broke out in the 11-ha citrus orchard of Mr. Li in Dayu County, Ganzhou City, Jiangxi Province. After being notified of the incident, the Ganzhou Chengfeng Intelligent Technology Crop Protection Team deployed the AGRAS T16 in their Fruit Tree Mode and successfully eliminated the red mites in just two days.  So, how exactly did they achieve that?

 

Background of Case Study

Citrus red mites are usually found on leaves, shoot tips, and fruit peels, sucking the saps of the plants and causing leaf and fruit falls. Since the pests can hide behind leaves, they bring great challenges to crop protection.

 

 

 

 

This operation took place on the rugged, hilly terrain in the south of Jiangxi Province. The focus was on a 11-ha citrus orchard spanning three adjacent hilltops, with steep slopes and an altitude difference of up to 60 m. Before this, spraying at the orchard was always done manually, which was inefficient and ineffective.

 

 

Operation date	July 2, 2019	Operation site	Dayu District, Ganzhou City, Jiangxi Province
Terrain	Mountain	Citrus variety	Newhall navel orange
Citrus tree height	Around 2.5 m	Tree age	4 years
Air temperature	25-30°C	Wind force	Level 1

 

 

Mission Steps

 

1.Surveying and mapping: mapping twice for better route accuracy

 

For the operation in Fruit Tree Mode, the first step was to map the orchard using Phantom 4 RTK (“P4R”). At a set flight altitude of 130 m, the aircraft took HD images of the orchard. Then, the mapping was done using DJI Terra. Due to the big altitude difference of the hilltops (>40 m), deviations would occur in the heights of the routes planned on the map. Therefore, a second round of mapping was necessary.

 

 

 

 

For the second time, the images generated by DJI Terra were imported into the P4R, which was then sent off on another aerial photography mission. This time, the aircraft flew in Terrain Follow Mode at an altitude of 70 m. Thereafter, the first step was repeated, followed by another round of mapping on DJI Terra.

 

After the map was generated, the team started planning the routes. As the large diameter of a citrus tree canopy (more than 4 m) cannot be sufficiently covered by the spray width under the Spot Spraying Mode, we used the Continuous Spraying Mode which involved generating a 3D flight path.

 

 

 

 

2. Pesticide preparation: combining various agents to ensure optimal crop protection

 

For the choices of pesticides, the team selected those with a strong systemic action, such as spirotetramat, which is effective against red mites on the back of citrus leaves.

 

On the morning of the operation, they prepared the pesticide mixture. Pesticides were added in turn into a 240L bucket using the dual dilution method. The sequence was to add the least soluble agents first followed by the highly soluble ones.

 

The following agents were used: 7 ml of 3% avermectin + 12% spirotetramat compound, 50 ml of Jianxiu mineral oil, and 5 ml of adjuvants, for each liter of water.

 

Avermectin is a broad-spectrum insecticide, miticide with stomach and contact poison effects; spirotetramat is an insecticide with bidirectional systemic action for targeting pierce-sucking pests such as mites, aphids, and thrips. The two compounds increases the pesticides’ efficacy against mites by attacking them from different points.

 

The Jianxiu mineral oil adheres evenly to the body surface of red mites, changing their behavior from crawling, feeding, mating, to spawning. This controls their harmful behavior and keeps them from reproducing. The adjuvants were added to improve the spread of the agents on the crop surfaces.

 

3. Operation: slow speed and high consumption per hectare is key

 

Remove the SD card from the computer, insert it into the remote controller, then import the measured routes into the remote controller. Set the operating parameters as per the table below to carry out a fully autonomous mission.

 

 

Operation mode	Fruit Tree Mode 2.0	Spraying mode	Continuous spraying
Flight altitude	2 m	Flight speed	2 m/s
Flow rate	2.5 L/min	Operating distance	3 m
Consumption per hectare	More than 60 L	Sprinkler model	XR11001VS

 

 

In this operation, the team set the flight speed much lower than that for field crops, while greatly increasing the quantity of pesticides used per hectare. A lower flight speed allows the pesticides to penetrate into the large canopies and dense leaves of the citrus trees, and reach the base and back of their leaves. With a high consumption per hectare, we can ensure that sufficient amounts of the pesticides are sprayed on the leaves. The two parameters are key to the protection of citrus crops.

 

 

 

Due to the complex terrain of the citrus farm, the pilot should constantly be aware of the aircraft’s flight status to avoid accidents.

 

 

Learnings From the Mission

 

 

The red mites began to die one day after the spraying. After a week, over 90% of them had been eradicated. After our operation, the orchard did not experience any red mite infestation in 2019. Based on the outcome of our mission, the team concluded several key factors for the protection of citruses against red mites.

 

1. Given the large canopies and dense leaves of citrus trees, increased spraying volume and lower flight speed are necessary to ensure thorough penetration.

 

2. For Gannan Navel Oranges, the typical flow rate applicable for trees under four years old is 2.5 L/min, those between four to eight years 3 L/min, and those over eight years 3.5 L/min.

 

3. Opt for pesticides with strong systemic action.

 

4. Orchards using drones require fewer rounds of pesticide spraying than those where spraying is done manually. Drones are also more efficient. A worker sprays around 0.7 ha a day, while a drone can cover 1.3 ha per hour.

 

Fruit trees have always been the toughest area in crop protection, but now a safe and efficient solution is available using the Fruit Tree Mode of DJI AGRAS aircrafts. As to how they can be used optimally, we also count on our users to constantly trial and explore in each and every unique scenario. Together with all its users, DJI Agriculture will continue to test and improve its products and services, to bring fruit tree productivity to the next level and achieve new breakthroughs in the industry.

 

 

 

Case Study Source:  Ganzhou Chengfeng Intelligent Technology Crop Protection Team