Key Takeaways
- Crop diseases cause farmers to lose between 20% and 40% of their crops worldwide.
- The most common crop diseases are fungal and bacterial.
- Management of crop disease requires careful monitoring and a prompt response to any infection.
- Continual monitoring using agricultural cameras helps in the early identification of crop diseases.
What Is Crop Disease?
A crop disease is any pathogen or agent that negatively affects crop health, development, or productivity.
Diseases are further defined as being infectious or noninfectious. Infectious plant diseases are typically caused by pathogens such as bacteria, fungi, viruses, parasitic plants, and worms. Noninfectious diseases include adverse growing conditions such as heat extremes, too little or too much moisture, soil toxicity, and mineral deficiencies.
For a plant disease to occur, three things must exist:
- A pathogen or causal agent.
- A susceptible host plant.
- A favorable environment.
Visible symptoms of diseased plants include dead or damaged tissue, abnormal growth, and incomplete or poor plant development.
Crop Diseases and Their Causal Agents
Worldwide, it’s estimated that between 20% and 40% of crops are lost due to disease, at a global cost of $220 billion. Pathogens causing plant disease are easily spread by the weather, birds, animals, farmworkers, farm equipment, and seeds. Common causal agents include bacteria, fungi, viruses, parasitic plants, and nematodes. Let’s review them in more detail, including types, causes, and disease control.
Plant Damage From Bacterial Infections
Pathogenic bacteria cause many plant diseases. They’re spread by insects, wind, rain, and farming implements. These single-cell microorganisms infect plants through plant glands, insect bites, and physical injuries from agricultural equipment and adverse weather.
Characteristics of Bacterial Plant Disease
Typical symptoms of a bacterial infection include soft rot, cankers, blights, scabs, and leaf spots. Bacterial infection also causes galls or growths on plant roots and stems.
Common Plant Bacterial Diseases
There are many bacterial diseases that infect crops, including:
- Goss’s wilt: A corn infection causing leaf blight and vascular wilt.
- Bacterial leaf streak: Also known as black chaff, it infects growing wheat and small grain crops.
- Common bacterial blight: This affects beans and peas, causing lesions that kill leaves and damage pods.
- Fire blight: A contagious disease that infects deciduous fruit.
Bacterial Disease Control
Bacterial diseases can be controlled through bactericides, the removal and disposal of waste, equipment sterilization, and obtaining pathogen-free seeds. Crop monitoring in agriculture is another helpful strategy; due to portable agri-cameras installed in the fields, it’s possible to detect disease symptoms early and take measures to prevent their spread.
Fungal Diseases
Fungi cause between 70% and 80% of all plant diseases. Fungi spores survive for months until germinated by high humidity. They’re spread by weather, irrigation, insects, and infected clothing.
Symptoms of Fungal Crop Disease
Symptoms include wilted and yellow plant leaves. Other signs include leaf spots, smuts, and leaf rust. Powdery mildew and white mold are common.
Fungal Diseases on Crops
Common fungal diseases include:
- Botrytis blight: A gray mold that causes fruits and plants to rot.
- Powdery mildew: A grayish-white powder infecting trees and grasses, causing leaves to wither and die.
- Corn smut: A fungal infection resulting in abnormal growths on leaves, tassels, and corn ears.
- Potato blight: A fast-spreading rot affecting leaves, stems, and tubers.
How to Manage Fungal Diseases
You can prevent infections by spraying crops with suitable fungicides. Crop rotation and planting healthy seeds also help prevent infection. Infected plants should be destroyed.
Viral Crop Diseases
Plant viruses are tiny organisms that replicate within plant cells. Small insects, including aphids, leafhoppers, and mites, transmit viruses to uninfected plants. Once a plant is infected, the virus multiplies, infecting adjacent plant cells.
Symptoms of Viral Plant Infections
Symptoms of viral infection include stunted plants and abnormal root, stem, and fruit growth. Leaves may be crinkled or have a mosaic pattern.
Viral Crop Diseases
Common plant viral diseases include:
- Tobacco mosaic: A widespread disease infecting many plants, including tobacco, tomatoes, and cucumbers.
- Barley yellow dwarf: This disease causes stunted growth and shriveled grain in wheat, barley, maize, and rice.
- Tomato spotted wilt: The wilt virus causes brown lesions on plant foliage and fruit.
- Prunus necrotic ringspot: This disease delays fruit maturity and causes fruit discoloration on plum and peach trees.
Controlling Viral Crop Diseases
Control is difficult and, in some instances, impossible. Infected plants should be destroyed and fields quarantined. Preventive measures include chemical spraying, crop rotation, and the planting of disease-resistant crops.
Diseases Caused by Parasitic Plants
Parasitic plants feed on their host plants, weakening and sometimes killing them. They cause stunted growth, wilting, and reduced plant yields.
Parasitic Plant Species
There are hundreds of parasitic plants, including:
- Mistletoe: Spread by seeds that stick to birds. Mistletoe seeds germinate through the bark of the tree and attach to its food supply.
- Dodder: This thread-like parasite traps plants and often infects fields of flax and clover.
- Witchweed: Small parasitic weeds that infect maize, sugarcane, and rice.
- Striga spp.: Tropical and subtropical parasites that can destroy cereal plants and sugarcane.
Managing Parasitic Plants
Control of parasitic plants includes the use of selective herbicides before seed production and by growing trap crops. Large infestations should be destroyed. In trees, prune infected branches.
Nematode Crop Diseases
Nematodes are tiny parasitic worms that infect plant roots. Using needlelike stylets, worms inject enzymes that digest plant material. Infected plants are susceptible to excessive moisture, drought, mineral deficiencies, and insect infestation.
Recognizing Nematode Crop Diseases
Symptoms of infection include yellowing, stunting, and diebacks. There’s a slow decline in plant health due to the destruction of the root systems. Once infected, nematodes spread rapidly.
Nematode Crop Diseases
Nematode-related diseases include:
- Root-lesion nematodes: These worms cause root lesions, leading to fungal or bacterial infection. They affect wheat, canola, mustard, and chickpea plants.
- Root-knot nematodes: These pests damage plant roots causing swelling and root rot. It impacts vegetables and fruit trees.
- Tylenchulus semipenetrans: They cause a slow decline in citrus trees, including destroying leaves and branches.
Controlling Nematode Diseases
Control measures include crop rotation, planting resistant species, and using soil fumigants. Careful application of hot water kills worms and their eggs. Other measures include plowing out roots of susceptible plants and planting cover crops.
How to Save Yields and Improve Crop Quality?
The early detection of crop disease is crucial to limit damage and minimize crop losses. Crop disease needs to be eradicated before it impacts produce quality. This is where agricultural cameras become valuable, allowing farmers to facilitate continuous crop monitoring and identify diseases early on. Using such technology, you can also monitor growth rates and localized weather conditions and determine the best time to treat crops with herbicides and fungicides.
