How Precision Technology can Tackle Cotton’s Irrigation and Pests’ Challenges in the 2020s

The high-value returns from cotton as well as the higher costs of production should be ample incentives for adopting precision farming. The vagaries of climate change and its disruptions to the normal farm schedule only increases the value of this information technology for cotton.

Climate Change is Altering Pest Attack Patterns

Increasing drought and extreme weather due to climate change are impacting cotton in unforeseen ways.

The unpredictable changes in weather patterns aren’t just disturbing the environmental conditions needed for cotton crops. Experts noticed since 2019 that the feeding and reproductive patterns of pests have changed. When wild plant hosts dry due to early drought, tarnished plant bugs (TPB) and stinkbugs move from them to cotton earlier than usual. So, instead of attacking cotton in mid-June, the tarnished bugs are now feeding and laying eggs on cotton plants earlier when the crop is developing young bolls.

The stinkbugs which survived and multiplied in a warm winter were on the cotton when it was flowering, and were also feeding on the young bolls. Though the pests are not new to cotton the timing of their attack and their sheer numbers is.

Alabama Cooperative Extension System’s entomologist Ron Smith said, “The plant bug situation is not one producers are unfamiliar with, but earlier action will be required to keep damage under control.”

Drought has also increased spider mites and whitefly populations, pests that can affect cotton quality.

Among the pests, those that feed on squares, bloom, and bolls are the ones that cause the most harm to the yield. These include the TPB, stinkbugs, whiteflies, bollworm, spider mites, and armyworms.

Pests like thrips attack young emerging cotton leaves and can delay crop maturity by 1-2 weeks and have to be treated prophylactically. From the pinhead square to bloom time, the Lyus bugs (which affect lint quality), spider mites, and bollworms, cause the most damage.

Cotton is a “Thirsty Crop”

Cotton is next only to rice in its need for water. Higher than normal temperatures have been accompanied by moderate to severe drought in several southern states, so irrigation assumes added importance to help cotton through future summers.

Figure 1: The crop evapotranspiration (ETc) varies during the growing season. Source: Cotton Incorporated

Growers anyway prefer to irrigate, since the lint yield from irrigated picker cotton is 1.24-1.44 times more, and from irrigated stripper cotton it is 2.49-2.89 times higher than dryland farms of the same category.

In the mid-south USA, 0.28 inch per day is supplied according to Cotton Incorporated. When the cotton plant is small it needs less water. As the plant grows, crop evapotranspiration (ETc), the water lost by leaf transpiration and soil evaporation, increases to a peak in the mid-season, as shown in Figure 1.

So far farmers have used the variation in ETc as the amount of irrigation that the crop needs, which during the growing season can be:

• 0.03 – 0.20 inch/day from 0-25 days of planting
• 0.22 inch/day at crop development
• 0.28 inch/day at mid-season with full canopy and maximum bolls

However, cotton farms are large and can have a lot of variation in soil chemical and biological properties and micro-topography. Therefore, the water retention capacity of soil will vary.

Need for Precision Farming

While irrigation and pesticide treatments are necessary, it is important to also prioritize efficiency by reducing costs to increase farm revenue. You should apply pesticides and irrigate only when needed, and depending on the intensity of stress.

A uniform application can oversupply or undersupply water and pesticides to cotton without increasing yield.

The frequent incidences of drought we are seeing will increase irrigation needs. Cotton growers, who have been using broad recommendations can use precision farming to finetune their irrigation to avoid higher water inputs and costs.

When irrigation is guided by plant needs and within-farm soil variation, it is possible to get more uniform yields by applying more water in drier areas and using less or no irrigation in wetter areas.

George Vellidis, crop and soil sciences professor at the University of Georgia, emphasizes this point, “We’ve been using …variable rate applications of fertilizers, plant growth regulators, defoliants on cotton and other inputs. So, the next big challenge is to address the parameter that affects all crops, and that’s water.”

Also, the pest situation is still evolving due to drought and previous recommendations of timing and dosage have to be adjusted. More data is, therefore, necessary and precision farming can provide it.

Precision farming also makes economic sense for cotton farms because they are usually large. Owned farms are on an average over 200 acres, while rented farms are twice as large and are over 475 acres. Even small savings per acre can improve returns on investment (ROI) considerably.

Combine IPM and Precision Farming

A combination of IPM and precision farming can reduce pesticide overapplication and development of pesticide resistance.

Integrated Pest Management (IPM) recommends the use of an ecologically suitable combination of biological and cultivation practices to reduce pest numbers and adding pesticides as a last resort.

Amanda Alworth’s recommendations for weed control can be applied for pests, and these practices should be followed for all farms, even those using Bt transgenic varieties, to prevent over-application of chemicals. 

Some practices that can be used to keep pest number down are:

• Timely planting and variety selection for assured early maturity of crops to shorten crop cycle and the possibility of pest damage
• Weeding and stalk destruction at least three weeks before planting to eliminate pests such as spider mites, cutworms, and wireworms
• Removing surrounding vegetation around the farm to eliminate natural habitats of bugs and spider mites
• Encourage natural predators and diseases of pests as part of biological control

Scouting Can’t Provide All the Information

Scouting regularly once a week in the early stages and twice a week after blooming by growers and crop consultants to check for insects is an integral part of IPM. With visual checks, you can see insects that are attacking blooms, squares, or bolls. To spot bugs, sweep net, beat bucket, or drop cloth are more useful. Insects per sweep are also used to estimate population build-up.

To track the changing pest populations due to drought, scout cotton fields earlier and at shorter intervals than usual, starting in mid-May.

While manual scouting is useful to spot incidence and identify pests, it is impossible to accurately calculate pest intensity and demarcate their infestation zones. 

Moreover, the economic threshold level where they cause enough harm to warrant action will differ from species to species, and multiple pest thresholds are difficult to establish.

Precision farming techniques come in handy by supplementing traditional scouting.

Applying Precision Farming Techniques

The helpful aspects of precision farming are data gathering and applying the information to make informed decisions for variable rate applications.

Gathering Information

Both pests and drought are forms of stress that can affect crop growth, its functions, and health. These changes can be tracked by various technology to gather information on the intensity of stress in a crop. There are two ways of gathering information on stress by tracking the changes in their functions through sensors or maps.

Map-Based Data

Map-based data involves taking remotely sensed images of fields, stitching them to get a seamless map of the entire farm, and then analyzing the image data. They are more commonly used than sensors for variable rate application. There are many approaches to get the necessary information.

• Stress maps based on spectral data show pests and drought incidence
• Yield maps point to variations in water-holding capacity within a farm

The remotely sensed imagery can be obtained from:

• Aerial photos, which are taken by drones from a low elevation. These can be high-resolution images made by RBG, NIR, multispectral, and hyperspectral cameras
• Satellite maps for high elevation imagery, which are available free of cost from several government agencies and give multispectral and hyperspectral images

There are several online software analysis providers, which identify patterns and quantify farms into zones of stress, based on intensities starting from none to medium and high. The maps also show the location of the pest attacks.

Sensor-Based

Instruments that have sensors are used to collect on-site data. These can be installed in the field or on tractors and drones. Portable ones can be used for data collection by people.

There are several soil probes for drought detection. The most recent probes are,

• Permanent smart internet-connected stations in fields
• A network of wireless soil moisture sensing nodes

These tools use numerous technologies to record water quantity and depth of availability with great precision.

Sensors that can record differences in chlorophyll levels, photosynthesis, transpiration, stomatal opening, and spectral signature of compounds can be used to detect both pest and drought stress.

Variable Rate Application

Prescriptive variable rate application for irrigation and pesticide treatments can be based on data from maps and sensors.

Pest Control

Using the analyzed map showing plant stress zones, a prescriptive map can be created by using software available for the purpose. To control pests, growers can choose the rate at which they want to spray. The maximum level is best for high pest infestations, and less for medium levels to get a variable rate prescriptive map for pesticide spraying. This map can be used with variable rate technology with or without a GPS-based controller on an implement or tractor.

Choose narrow target pesticides that are not harmful to beneficial insects and predators, instead of broad-spectrum pesticides that build resistance.

Variable Rate Irrigation

New Variable Rate Irrigation (VRI) technology allows farmers to turn off and regulate water amounts.

• Irrigation zones can be created for variable rate applications based on yield maps or stress maps
• In dynamic VRI, soil probe data is used. Soil probes have data that is analyzed by accompanying software to give information on precise soil moisture levels and recommendations on irrigation amounts. Probes with telemetry can send the data remotely to connected computers or smartphones. So water, based on real-time plant needs can be provided to the crop

The equipment that is needed for applying irrigation or chemicals will have to be different, and new generation equipment that can be retrofitted  to  old machinery is already available on the market.

Precision Farming Users in Cotton

Global warming is here to stay and the challenges it throws up can only be met by changing current farming operations. Luckily, the number of people who use precision farming to produce cotton has been rising in the past two decades. However, people find the continuously evolving technology difficult to follow and use. Hence, it is best to work with crop consultants who can organize turnkey solutions, and also help in variable rate application calculations. The additional cost of using precision farming methods is offset by an improvement in ROI.