Plant Diseases in the Philippines: Causes, Signs and Prevention

Diseased in Tagalog is may sakit, and a sick plant is halamang may sakit. Sakit means illness or disease, so farmers call plant diseases sakit ng halaman. Mildew in Tagalog is amag, the same word for mold on bread. Rice blast, for example, is mata mata in Bisaya and agupaw in Waray.

The four causes of plant diseases and how each looks

Fungi cause many of the worst crop diseases, and their spores travel by wind, water, insects, seed, soil and tools. Water molds, or oomycetes, look like fungi but form a separate group that thrives in wet weather. Bacteria are single cells that enter through wounds and natural openings. Viruses and viroids multiply only inside living cells, and insects carry many of them. Finally, nematodes are tiny soil worms that feed on roots.

A symptom is how the plant reacts, such as yellowing. A sign is the germ itself: fungal growth, sclerotia or bacterial ooze. For example, the test for bacterial leaf blight is to stand a cut lesion in clear water and watch for cloudy streams.

How plant diseases spread

• Seed. Bakanae and brown spot ride on rice seed. The brown spot fungus survives in seed for more than four years.
• Soil. Fusarium wilt, clubroot and root knot nematodes wait in the soil for the next crop.
• Water. Irrigation water spreads bacterial leaf streak, and the resting bodies of sheath blight float from hill to hill.
• Wind and rain. Blast spores travel far in the air, and rain splashes bacterial leaf blight around.
• Insects. The green leafhopper carries tungro, and the brown planthopper carries grassy and ragged stunt. The banana aphid spreads bunchy top, and the whitefly spreads tomato yellow leaf curl.
• Tools and planting material. Bacteria survive on tools, and a sick sucker or seedling brings the disease along.

The worst diseases by crop

For rice, see our rice diseases guide. Against corn downy mildew, use resistant varieties, plant early and together with the farms around you, and grow no corn near sugarcane, sorghum or talahib grass.

Disease, pest or hunger? Tell them apart

Pests leave evidence: the insect, its eggs, chewed holes or droppings. Diseases leave symptoms and often signs, and they spread to neighboring plants over days. Nutrient problems and chemical burns do not spread, and they often hit a large area at once.

Some look alikes fool even old hands. Rice with tungro turns yellow and stunted, like rice short of nitrogen or zinc. Kresek, the seedling form of bacterial leaf blight, looks like stem borer damage. Yet a kresek plant does not pull out easily. Ask these questions before you buy anything.

1. Where is it? A whole field at once points to nutrients, water or chemicals. Growing clusters point to a disease.
2. Is it spreading? Mark sick plants and look again in a few days.
3. What stage is the crop? Many diseases strike at one stage, like tungro on young rice.
4. What else is there? Look for insects, eggs and spray drift.
5. What did you do? Recall the fertilizer, water, variety and last season's problems.

Still not sure? Take a clear photo in daylight and ask Anee, the smart farm technician in anee.io. She answers in Tagalog or English, and she reads your lot's growth stage first. Treat her answer as a first opinion, and call your municipal agriculturist for a serious outbreak.

Prevention first

A disease needs three things at once: a virulent germ, a susceptible plant and favorable weather. Take away any one and the disease stalls. That is why prevention beats any spray.

• Plant resistant varieties. Resistance is the most widely used control. Ask your DA office which ones resist the diseases your farm had before.
• Use clean seed and planting material. Certified seed, inspection and quarantine keep germs off new land.
• Plant with your neighbors. Planting within a month of the usual local date keeps insect borne viruses like tungro low.
• Feed in balance. Too much nitrogen raises blast, sheath blight and bacterial leaf blight. A lack of potassium invites brown spot.
• Give plants air. Wider spacing and good drainage keep leaves drier, and moisture helps spores sprout.
• Clean up and rotate. Plow under sick stubble and remove sick plants early. Rotation with non host crops works well against root knot nematodes.

Timing is half of prevention. The anee.io cropping calendar dates your scouting days from each lot's own day zero. Its growth stages view lists what to watch for on any date.

Fungicide groups (FRAC) and why you rotate them

A fungicide is made for fungi and water molds. It does not cure a virus, and chemicals against bacterial leaf blight are neither economical nor effective. Contact fungicides protect the leaf surface, while systemic ones move into the plant.

FRAC, the Fungicide Resistance Action Committee, gives every active ingredient a group code meant for the label. The group tells you how it works and how fast fungi learn to beat it.

Fungi adapt. If a fungus resists one member of a group, FRAC warns, it will most likely resist the others too. So two brands with the same group number count as one spray. Switch groups for the next application, and lean on the low risk M groups. For example, repeated benomyl seed treatment lets the bakanae fungus build resistance. Our fungicide guide explains more.

Questions about plant diseases