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close this book Agricultural development workers training manual - Volume III Crops
close this folder Chapter III: Technical guidelines and references for the crops training component
Open this folder and view contents Units of measure and conversions
Open this folder and view contents Surveying and interpreting the agricultural environment
View the document A guide to troubleshooting common crop problems
Open this folder and view contents Guidelines for vegetable growing
Open this folder and view contents Introduction to insects and insect control
View the document Some "organic" (non-chemical) pest controls
Open this folder and view contents Using chemical insecticides
Open this folder and view contents Disease control
Open this folder and view contents Nematodes and their control
View the document Weed control

A guide to troubleshooting common crop problems

It takes a lot of practice and detective work to accurately troubleshoot crop problems. Some abnormalities like wilting or leaf yellowing can have numerous causes.

How to Troubleshoot: First, learn to distinguish normal from abnormal growth when you walk through a farmer's field. Keep a close watch for telltale trouble signs such as abnormal color, stunting, wilting, leafspots, and signs of insect feeding. Make a thorough examination of affected plants, including the root system and the inside of the stem, unless the problem is obvious. Obtain detailed information from the farmer concerning all management practices that might have a bearing on the problem (i.e., fertilizer and pesticide applications, name of crop variety, etc.). Note whether the problem occurs uniformly over the field or in patches; this can provide valuable clues; since some problems like nematodes and poor drainage seldom affect the entire field.

Troubleshooting tools, etc.

1. A pocketknife for digging up seeds or slicing plant stems to check for root and stem rots or insect borers.

2. A shovel or trowel for examining plant roots or checking for soil insects or adequate moisture.

3. A pocket magnifying glass to facilitate identification of insects and diseases.

4. A reliable soil pH test kit for checking both topsoil and subsoil pH; especially useful in areas of high soil acidity. Beware of cheap kite, especially those using litmus paper. The Hellige Truog kit is one of the beat ant costs about $15 (U.S.).

5. Disease, insect, and hunger signs guides: Refer to the Bibliography an the end of the Crops Guidelines.

TROUBLESHOOTING GUIDE

CROP APPEARANCE

PROBABLE CAUSES

POOR SEEDLING EMERGENCE

Low germination seed

(Carefully dig up a section of row and

Planting too deep or too shallow

look for the seeds)

Soil crusting or overly cloddy soil

 

Lack of moisture

 

Clogged planter

 

Seeds washed out by heavy rain

 

Fertilizer "burn"

 

Pre-emergence damping off disease

 

Birds, rodents

 

Seed eating insects (wireworms, seed corn maggots, seed corn beetle)

WILTING

(Pull up a few plants carefully using a shovel

Actual lack of moisture due to drought or poor irrigation management (watering too lightly or too infrequently).

or trowel and examine the root; check stem for borers or rotted or discolored tissue.)

Diseases (bacterial or fungal wilts; certain types of root and stem rots).

 

Very high temperatures, especially if combined with dry, windy conditions.

 

Root feeding insects

 

Stem borers

 

Weed competition

 

Root pruning by hoe or cultivator

 

Nematodes (especially if confined to patches and when plants wilt despite having sufficient water).

 

Stem breakage or kinking

LEAF ROLLING OR CURLING

Lack of moisture (maize, sorghum, millet)

 

Virus

 

Sucking insects feeding on stem or leaves

 

Boron, calcium deficiency (beans only)

 

Verticillium wilt (peanuts)

LEAF CRINKLING, PUCKERING

Aphids, leafhoppers feeding on leaves or stems

 

Virus

LEAF "BURNING" OR BROWNING

Drought

 

Excessive heat

 

Fertilizer burn

 

Insecticide burn

 

Dipterex, Azodrin (Nuvacron), or methyl parathion injury on sorghum

 

Herbicide damage

 

Nutrient deficiency

 

Aluminum, iron, or manganese toxicity due to excessive acidity (below pH 5.5). Salinity or sodium problems (confined largely to low rainfall areas, especially if irrigated.) Boron toxicity from irrigation water (low rainfall areas) or improper placement of fertilizer boron.

LEGGY, SPINDLY PLANTS

Lack of sunlight caused by overcrowding or long periods of heavy cloudiness.

HOLES IN LEAVES

Caterpillars

 

Beetles

 

Earwigs

 

Crickets

 

Snails, slugs, especially on beans (check for slime trails)

 

Breakdown of dead tissue due to fungal or bacterial leafspots

SPOTS ON LEAVES

Fungal or bacterial leafspots

 

Virus

 

Sucking insects

 

Spilling of fertilizer on leaves

 

Herbicide spray drift, especially paraquat (Gramoxone)

 

Sunscald (beans)

LEAF MALFORMATION WITH STEM CURVING & TWISTING (Broadleaf plants only)

2, 4-D type herbicide damage due to spray drift or a contaminated sprayer (broadleaf crops only).

LEAF MOTTLING, LEAF

Virus

MALFORMATION, PLANT

 

MALFORMATION

 

LEAF STRIPING

Nutrient deficiency

 

Virus

 

Genetic

YELLOWING, STUNTING

Nutrient deficiency

 

Poor drainage

 

Nematodes

 

Low pH (excessive acidity)

 

Root rot, stem rot, Misc. diseases

OVERNIGHT DEFOLIATION OF PLANTS

Leaf cutter ants, grazing animals

PLANTS CUT OFF AT

Cutworms

OR NEAR GROUND LEVEL

Mole Crickets

TWISTING TUNNELS IN LEAVES

Leaf miners

YOUNG SEEDLINGS COLLAPSE NEAR GROUND LEVEL AND DIE

Fungal seeding blights, damping off, Heat girdling of stem (beans)

POOR GROWTH, LACK OR VIGOR

Too dry or too wet

 

Too hot or too cold

 

Insects, diseases

 

Weeds

 

Unadapted variety

 

Low pH

 

Salinity-alkalinity problems

 

Overcrowding

 

Shallow soil

 

Soil compaction, hardpan

 

Poor drainage

 

Nutrient deficiency

 

Faulty fertilizer practices

 

Nematodes

 

Excessive cloudiness

 

Herbicide carryover

 

Overall poor management

 

Damaged seed (beans)

LODGING OR STALK BREAKAGE (Maize,

Overcrowding

Sorghum, Millet)

Stalk rots

 

Rootworms

 

High wind

 

K deficiency

POOR NODULATION ON PEANUTS, COWPEAS, SOYBEANS, OTHER LEGUMES THAT ARE EFFICIENT FIXERS (Carefully dig up the root system and check for nodulation; Clusters of fleshy nodules, especially on the Taproot, and with reddish interiors are signs of good nodulation. Don't confuse nodules with nematode galls!)

Soil lacks the correct type of Rhizobia; seed inoculation is needed. Improper inoculation: wrong strain, innoculant too old or improperly stored.

Exposure of inoculated seed to excessive sunlight or contact with fertilizer or certain seed treatment fungicides.

Excessive acidity (soybeans are especially susceptible to Molybdenum deficiency).

Plants are too young (it takes 2-4 weeks after plant emergence for the nodules to become visible).