Plant Problem Diagnosis
- Ting Ting
- Nov 1, 2021
- 6 min read
Updated: Feb 10, 2022
Plant problems often involve the interaction of two or more causes.
Hot, dry conditions encourage a buildup of two-spotted spider mites.
High fertility and excessively dry soil can intensify soluble salt problems.
Diagnostic Tools:
Light meter
Thermometer
10-20x magnifying glass
Knife/shears
Hygrometer
Solubridge
Hand pH meter
Regularly inspect plants for:
Whiteflies - look on lower leaf surfaces
Scales - look on upper/lower leaf surfaces / stems
Mealybugs - attack all plant parts, including roots, often found clustered on stem tips or new growth
Symptoms | Possible Causes | |
Brown leaf margins / tips Chlorosis Dropping leaves | | Root problems |
Change. leaf colour General yellowing Chlorosis |  | Improper light level (too high / too love) Excessive high temperature Nitrogen deficiency |
Chlorosis on young leaves |  | Deficiency of iron, manganese, copper, zinc Phytotoxic response to pesticides |
Yellow spots on leaves |  | Cold water injury Viral or fungal infection Phytotoxic response to pesticides or fertilisers, air pollutants, eaf injury or light intensity that is too high |
Round spots on leaves |  | Fungal, bacterial infection Phytotoxic response to pesticides, fertilisers or air pollutants |
Variegated leaves change to green |  | Low light Excessive fertiliser Genetic changes |
Mosaic or new colour pattern |  | Virus infection Cold water injury Phytotoxic response to pesticides |
Speckled, stippled pattern on leaves |  | Spider mites Thrips |
Water-soaked or greasy appearance of leaves |  | Temperature injury (high / low) Bacterial or fungal infection Foliar nematodes |
Leaf margins or tips turn brown |  | High salinity High/low temperature injury Low relative humidity Pesticide phytotoxicity Feeding of spider mites
|
Brown, dead areas within leaf blade |  | Fungal, bacterial infection Cold water injury Leaf miners Phytotoxic response to pesticides or fertilisers Foliar nematodes |
Brown leaf margin Brown areas within leaf |  | Cold air injury Water damage Phytotoxic response to pesticide or fertiliser |
Excessive leaf drop |  | Low light response High soil salinity Too much or inadequate water |
Unusual holes in the foliage |  | Feeding of insects, slugs or snails |
Grayish-white powdery coating on leaves |  | Powdery mildew |
Clear, sticky residues on leaves |  | Mealybugs, aphids, whiteflies, scale insects |
Black, velvety residue on leaves |  | Sooty mold fungus Algal growth (if green) |
Excessive soluble salt Stunted growth Foliage wilt (even when soil is moist) Chlorotic leaves Brown tips and margins | Reduces root water absorption In severe cases, water may be reabsorbed by the growing medium | Using poor quality water (high in magnesium, calcium, chlorides and carbonates) Excessive fertilisation Poor drainage and aeration Improper watering Drainage water not removed |
| |
NATURAL REMEDIES:
Chrysanthemum Spray
For treatment of a broad range of insects; works as a repellent
Ingredients:
• 300 g fresh chrysanthemum flowers or;
• 100 g dried chrysanthemum flowers
• 4 litre hot water
Steps:
1. Add the chrysanthemum flowers to water and boil for 20 mins
2. Soak for 24 hours
3. Sieve out the residue and pour liquid into the spray bottle
4. Spray on the affected areas
Eco-Enzyme Spray
For treatment of a broad range of insects; works as a repellent
Ingredients:
• 300 g vegetables or fruit waste
• 100 g brown sugar
• 1 litre water
Steps:
1. Add brown sugar into the container
2. Add f water
3. Stir will until fully dissolved
4. Add vegetable or fruit waste and mix well
5. Seal the container and label with the date
6. During the first month of fermentation, stir the mixture twice a week to release gas created during fermentation
7. Allow fermentation to continue for another 2 months, stirring the mixture weekly to fortnightly
8. After 3 months, the mixture will be ready for use. Sieve out the residue and pour liquid into another container
9. Dilute the liquid with water before use. Start with a more diluted solution. Recommend ratio is 1 part liquid per 100 parts water.
Use magnifying glass to check for insects:
Soft, armoured scale insects - Small, imobile insects with sucking mouths. Found attached to leaves or other plant surfaces. Usually brown, black or grey in colour.
Soft-bodied, sap-sucking insects. Most commonly found on new growth but can be present in other plant parts, including roots.
Two-spotted spider mites - fine-silky webbings on leaves or stems. Leaves often take on a stippled, silver or dusty appearance.
SYMPTOMS: Tiny pale specks on leaves or light, white webbing on leaves or buds.
PREVENTION: Always give a new plant a thorough bath on tops and bottoms of leaves and quarantine it for a week. Spider mites need dry conditions.
NATURAL REMEDY:
Baking Soda and Water Solution Spray
For treatment of red spider mites and some fungal diseases
Ingredients:
• 1 tbsp baking soda
• 1 litre water
Steps:
1. Mix all ingredients together
2. Pour into spray bottle
3. Spray on the affected areas
Sucks plant sap, leaving sticky deposits of honeydew often on lower leaf surfaces.
SYMPTOMS: Stunted or twisted leaves, white spots or black moldy areas on the top of foliage.
PREVENTION: Whiteflies are drawn to the color yellow. Set up sticky traps to capture them and as an early warning system to prevent widespread infestation.
NATURAL REMEDY:
Citrus Spray
For treatment of whiteflies
Ingredients:
• Orange or lemon peels
• 1 litre water
Steps:
1. Boil water
2. Remove from heat and add peels
3. Cover and steep until cool
4. Sieve out the residue and pour liquid into spray bottle
5. Spray directly on the pests
Tiny, wingless or winged insects. Attack tender, young leaf parts, leaving them distorted, silvery-flecked with black fecal material on heavily infected surfaces.
SYMPTOMS: Silver or bronze colored streaks on leaves, which eventually turn brown, dry and crumbly.
PREVENTION: Check often for the presence of thrips by giving plants a gentle shake. The larva are wingless and will leap when jarred. Apply neem immediately when you see the pests to stop this fast-growing population.
NATURAL REMEDY:
Onion, Garlic and Chilli Spray
For treatment of thrips, aphids, caterpillars, and leaf-eating insects; works as a repellent.
Ingredients:
• 2 bird’s eye chilies, chopped
• 2 large onions, chopped
• 2 bulbs garlic, chopped
• 1 litre water
Steps:
1. Combine all ingredients
2. Mix with water and allow to steep for 24 hours
3. Sieve out the residue and pour liquid in spray bottle
4. Spray on the top and underside of the leaves
5. Solution can be stored for 2 weeks in a dark place
MORE INFO:
APHIDS
SYMPTOMS: Leaves develop yellow spots, then wilt. Black mold growing on top of leaves.
PREVENTION: Aphids produce as many 12 new offspring per day. Use insecticidal soap spray twice – once for the first application then 5 to 7 days later to get the next generation. Check underneath leaves every week to catch any new infestations.
NATURAL REMEDY:
Onion, Garlic and Chilli Spray (see above)
BROAD MITES
SYMPTOMS: New leaves are small, stunted, strap-like and sometimes curl downward and inward in response to broad mite feeding. Prolonged feeding will stunt and reduce plant growth, increases shoot proliferation down the stem, and sometimes causes a leaf colour change. Broad mite saliva is toxic to plants, and even after the mites are destroyed, new growth may still emerge deformed.
new plant growth may be twisted or bent
the leaf may be, blistered, or wet-looking
in the flowering stage, its bud would be sickly and eventually dies
turned up edges of the leaves
the leaves may turn yellow and die
scars on the surface of the fruit
PREVENTION: Broad mites feed on the tight and new growth, so check the newest growth first. It is critical to control broad mites as quickly as possible.
POWDERY MILDEW
SYMPTOMS: White to gray powdery coating, especially on young leaves. Blistered areas on leaf edges that causes them to curl upward. Eventually, severely infected leaves turn brown -- the coating blocks light from reaching them -- then drop. Flower buds may be white on the outside and never open.
CAUSE: Dampness and a highly humid environment with little ventilation.
PREVENTION: Increase ventilation. Use fans to refresh air and keep humidity in check.
NATURAL REMEDY:
Milk Solution Spray
For treatment of powdery mildew
Ingredients:
• 1 part milk
• 10 parts water
Steps:
1. Mix the milk with water
2. Pour in spray bottle
3. Spray directly on the affected areas
NITROGEN DEFICIENCY
SYMPTOMS: Lower leaves look yellow and become soft and curl inward, then turn brown and crispy before falling off completely.
CAUSE: Nitrogen deficiency always affects the oldest (lowest) leaves first. As plants get close to harvest, it's normal for them to show signs of a nitrogen deficiency as the plant to direct all of its energy into the fruit or flowers rather than growing new leaves.
QUICK FIX: Give plants in their vegetative growth stage a high-nitrogen nutrient formula such as fish tankage (decomposing processing waste) fertiliser to deliver a strong dose of nitrogen in a form that plants absorb and use quickly.
PREVENTION: A regular dose of an amino-acid supplement to give the plants a constant nitrogen fix. Amino acids are building blocks of protein that help plants take up and use nitrogen.
PHOSPHORUS DEFICIENCY
SYMPTOMS: Lower leaves look dark green or bluish and appear shiny. May have splotches that look brown or bronze. Affected leaves curl downward. Phosphorus deficiency usually shows up first at the bottom of the plant (on the oldest leaves) and progressively climbs up the plant if untreated.
CAUSE: For many crops, the need for phosphorus peaks during the transition from vegetative growth to budding.
QUICK FIX: When your plants near their full-grown size add bone meal-based supplements, which are rich in phosphorus. Bone meal is a natural source of phosphates in a form that plants absorb and use readily.
PREVENTION: Cooler temperatures and temperature fluctuations can inhibit plants' ability to absorb phosphorus. Keep the temperature consistently between 18 degrees C and 23 degrees C.
POTASSIUM DEFICIENCY
SYMPTOMS: Leaves all over the plants are yellow or brown, with tips and edges that appear burned, while the veins remain green.
CAUSE: Plants need high levels of the nutrient especially during their budding and flowering stages.
QUICK FIX: Switch to a high-potassium fertilizer during the budding phase of plants' growth. Molasses in the formula helps plants take up and use the potassium.
PREVENTION: For soil-grown plants, be sure the pH is 6.0 to 7.0 and for hydroponic crops keep the pH to 5.5. to 6.5.
HEAT STRESS
SYMPTOMS: Edges of leaves curl inward and form a cup. The upper leaves are most affected.
CAUSE: Heat stress causes rapid evaporation, so plants curl up to conserve moisture. Plants too close to high-intensity lights are prone to heat stress, but it can be a problem in any room where temperatures are persistently above 26 degrees C.
QUICK FIX: Set up fans to blow out hot air and bring in cooler fresh air.
PREVENTION: Monitor the temperature. Maintain constant ventilation.
OVERWATERING
SYMPTOMS: Drooping leaves, curling downward from the stem to the tip.
CAUSE: Inadequate drainage or watering hydroponic plants too frequently.
QUICK FIX: Allow plants to dry out and then gradually increase water as plants recover.
PREVENTION: Water soil-grown plants only when the top inch of the soil is dry (stick your finger in it to check). Be sure excess water drains away quickly from plants' roots in pots or in flush-and-drain hydroponic systems. Don't put small plants in big containers, because the soil will hold extra moisture that the roots cannot absorb.
Sources:
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