String bean Nutrient Deficiency: Signs, Causes and the Fertilizer That Fixes It
String bean nutrient deficiency is one of the first things to check when the leaves of your sitaw (string bean) turn yellow, purple or burnt at the edges. On Philippine farms the usual ones are nitrogen, phosphorus, potassium, magnesium, boron and manganese. This guide shows where each one starts, how to be sure, and the fertilizer that fixes it.
Start with one question: did the change begin on the old leaves or on the young ones? Nitrogen, phosphorus, potassium and magnesium move inside the plant, so a shortage shows on the old, lower leaves first. But boron and manganese stay where the plant first put them, so the young leaves and the growing tip show it first. After that, the color and the pattern narrow down which string bean nutrient deficiency you have, and a soil test confirms it. Each one below has its signs, its causes and its fix.
String bean nutrient deficiency signs, old leaves and young leaves
Shows first on the old leaves
| Nutrient | Where it starts | What you see | Fix with |
|---|---|---|---|
| Nitrogen | old, lower leaves, the whole plant | Vines grow weak and light green, lower leaves yellow, and the roots have few working nodules. | Rhizobium inoculant for cowpea and sitaw, Urea 46 0 0 |
| Phosphorus | old, lower leaves, the roots | Slow, short, dark green vines with few flowers and pods. | 16 20 0, Complete 14 14 14 |
| Potassium | old, lower leaves, leaf edges and tips | Older leaflets yellow at the tips and edges, then brown, while pods stay short. | Muriate of potash 0 0 60, Complete 14 14 14 |
| Magnesium | old, lower leaves, between the veins | Older leaves yellow between green veins, then deep yellow with rusty specks. | Epsom salt / magnesium sulfate, Dolomite |
Shows first on the young leaves
| Nutrient | Where it starts | What you see | Fix with |
|---|---|---|---|
| Boron | young leaves and the tip | Top leaves crinkle and stay small, and flowers drop. | Borax |
| Manganese | young leaves and the tip, between the veins | New leaves pale between green veins, often where lime was spread heavily. | Manganese sulfate |
Before you buy fertilizer for a string bean nutrient deficiency
So use the table to pick the likeliest string bean nutrient deficiency, then read its section below. Also keep in mind that dry soil, standing water, cold nights, a pest or a disease can look the same. That is why it pays to check the roots and the whole field first.
Nitrogen deficiency in string bean
Lower leaves turn pale and yellow and the vines climb slowly with light green leaves and few pods. Sitaw fixes its own nitrogen through root nodules, so this usually means poor nodulation. You see it most at this stage: three to six weeks after planting, before heavy flowering.
Why nitrogen deficiency happens in sitaw
In a legume this usually means poor nodulation: no inoculant in a field new to the crop, inoculant killed by sun or heat, very acid soil, waterlogging, hot dry soil, or too much nitrogen fertilizer near the seed, which stops nodules from forming.
How to tell it apart
Sulfur deficiency yellows the young leaves first. Iron and manganese deficiency yellow between green veins on young leaves. To be sure, dig, do not pull, a few plants 3 to 6 weeks after planting, wash the roots and cut some nodules open. Pink to red inside means they are working, white means not active yet, and brown, grey or mushy means dead. Yellow plants with few or dead nodules point to a nodulation failure, not a lack of fertilizer.
What to apply for nitrogen deficiency
Feed the crop now with a light sidedress of Urea 46 0 0 or Complete 14 14 14 beside the plants, following the soil test, since new nodules cannot be added to a standing crop. If the nodules failed, 10 to 20 kg of nitrogen per hectare is enough: about half a bag of Urea 46 0 0 beside the rows, before flowering.
- Rhizobium inoculant for cowpea and sitaw
- Urea 46 0 0
- Complete 14 14 14
Sold here with nitrogen: Atlas Granular Urea (46 0 0) by Atlas Fertilizer, Crown Champion Ammonium Sulfate by Aqua Hydroponic Prime Ventures (21 0 0 with 24 percent sulfur), Agripower 46 0 0 (Locally Blended) Coated by Green Acres Agri Tech and Calcipro by Ramgo (15.5 0 0 with 18.8 percent calcium). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to urea fertilizer, and the page on nitrogen deficiency in every crop. In anee.io, Anee, the smart farm technician, reads a photo of the leaf and tells you which nutrient is short.
To keep it away, rhizobium inoculation improves nodules and cuts nitrogen needs. Coat the seed at planting and keep the soil pH at 5.5 to 6.5. Keep organic matter up with compost, manure or crop residues.
Phosphorus deficiency in string bean
Vines grow slowly and stay short, with dark or bluish green leaves and few flowers and pods. Roots and nodules are small. You see it most at this stage: seedling to first harvest.
Why phosphorus deficiency happens in sitaw
Acid soils and soils low in phosphorus. A pH of 5.5 to 6.5 is best for long bean.
How to tell it apart
Nitrogen deficiency makes leaves pale, not dark. To be sure, soil test for phosphorus before planting.
What to apply for phosphorus deficiency
Apply 16 20 0 or Complete 14 14 14 at planting, following the soil test. For a standing crop give a 2 percent DAP 18 46 0 spray (20 g per liter, 320 g in a 16 liter sprayer) every 15 days for pulses. A usual basal dose is 2 to 3 bags of Complete 14 14 14, or 1 to 2 bags of Diammonium phosphate 18 46 0, per hectare in the furrow at planting.
- 16 20 0
- Complete 14 14 14
- Diammonium phosphate 18 46 0
Sold here with phosphorus: Philphos 18 46 0 (Di Ammonium Phosphate), Atlas Super Gro (16 20 0) by Atlas Fertilizer, Amigo Planters Granular Single Super Phosphate by La Filipina (0 18 0 with 11 percent sulfur) and Triple Super Phosphate by Newman Chemicals (0 46 0). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to 16 20 0 fertilizer, and the page on phosphorus deficiency in every crop.
To keep it away, mix phosphorus and compost into the planting holes or rows each season.
Potassium deficiency in string bean
The tips and edges of older leaflets turn yellow, the yellow spreads toward the center. The edges die and brown before the leaves drop. Sitaw is the same species as cowpea, so the signs match. Pods stay short and thin. You see it most at this stage: flowering and the long harvest period.
Why potassium deficiency happens in sitaw
Sandy soils, long picking seasons that take a lot of potassium away, and no potash in the program.
How to tell it apart
Magnesium deficiency yellows between the veins of old leaves, not the edges. To be sure, soil test for potassium.
What to apply for potassium deficiency
Sidedress Muriate of potash 0 0 60 or Complete 14 14 14 following the soil test. Give a 1 percent potassium chloride spray (10 g per liter, 160 g in a 16 liter sprayer) for cowpea type beans. A usual dose is 1 bag of Muriate of potash 0 0 60 per hectare at planting.
- Muriate of potash 0 0 60
- Complete 14 14 14
Sold here with potassium: Atlas Muriate of Potash (MOP) by Atlas Fertilizer (0 0 60), Simplot Sulfate 0 0 50 by Nutranta, Potassium Nitrate by Parafield (13 0 46) and Qrop Mix Production 14 0 23 plus 13 Cao by Farmtech Agriland (14 0 23 with 9.3 percent calcium). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to potash fertilizer, and the page on potassium deficiency in every crop.
To keep it away, feed potash again during the picking season on sandy soils. Keep organic matter up with compost, manure or crop residues. Split the potash on sandy soil.
Magnesium deficiency in string bean
Areas between the veins of older leaves turn yellow, then deep yellow with rusty specks and dead blotches. Sitaw is the same species as cowpea, so the signs match. You see it most at this stage: mid season, during heavy picking.
Why magnesium deficiency happens in sitaw
Acid sandy soils and heavy potash use.
How to tell it apart
Potassium deficiency starts at leaf edges and tips. To be sure, soil test for magnesium and pH.
What to apply for magnesium deficiency
Give a 1 percent magnesium sulfate spray (10 g Epsom salt per liter) every 15 days for cowpea. Use Dolomite on acid soils as the soil test advises. A usual dose is 100 to 150 kg of Kieserite or 150 to 200 kg of Magnesium sulfate per hectare at planting. On acid soil, 1 to 2 tons of Dolomite mixed in before planting both limes and feeds.
- Epsom salt / magnesium sulfate
- Dolomite
Sold here with magnesium: Dolomite by A6 Agrisource (24 percent calcium and 11 percent magnesium), Agsmart Kieserite Granule (20 percent sulfur and 16.3 percent magnesium), DDDD Planter's Choice Magnesium Sulphate Monohydrate by Modern Time (15.1 percent magnesium) and Zetryl MAG 9 by Zetryl Chem (9 percent magnesium). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to complete fertilizer, and the page on magnesium deficiency in every crop.
To keep it away, lime acid soils with dolomite before planting. Keep potash in balance with magnesium and calcium.
Boron deficiency in string bean
Young leaves crinkle and stay small, and the vine top grows poorly. Sitaw is the same species as cowpea, so the signs match. You see it most at this stage: flowering and pod set.
Why boron deficiency happens in sitaw
Sandy soils low in organic matter, high pH soils and dry spells.
How to tell it apart
Virus diseases crinkle leaves too, but with a yellow and green mosaic. To be sure, leaf or soil test for boron. In a soil test, less than 0.5 ppm of boron is low.
What to apply for boron deficiency
Give a 0.2 percent borax spray (2 g per liter, 32 g in a 16 liter sprayer) for cowpea. Keep boron out of the seed row. A usual soil dose is 5 to 10 kg of Borax per hectare (0.5 to 1 kg of boron), mixed evenly with the basal fertilizer.
- Borax
Sold here with boron: Etifert 11 (Borax Decahydrate) by Zetryl Chem (11 percent boron), Fertibagra 15G by Unilox Far East Resources (14.6 percent boron), B17 (Boric Acid) by Newman Chemicals (17 percent boron) and Better Yield by Bacphil Planters Fertilizer (0 0 0.9 with 10 percent boron). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to foliar fertilizer, and the page on boron deficiency in every crop.
To keep it away, add compost and water evenly at flowering. Test the soil every two or three years. Never repeat boron without a test.
Manganese deficiency in string bean
Leaves turn pale green to yellow between green veins, starting on the young leaves, with brown spots later. Sitaw is the same species as cowpea, so the signs match. You see it most at this stage: early growth.
Why manganese deficiency happens in sitaw
High pH, over limed sandy soils and soils high in organic matter. Beans need much manganese.
How to tell it apart
Iron deficiency turns the veins yellow too. To be sure, leaf test and soil pH. In a soil test, less than 1 ppm of manganese is low.
What to apply for manganese deficiency
Give 5 kg manganese sulfate per hectare to the soil or two sprays 10 days apart for cowpea. Spray beans with about 1.1 kg of manganese per hectare. Spray Manganese sulfate at 0.2 to 0.5 percent (32 to 80 grams in a 16 liter sprayer) two or three times, 10 to 14 days apart.
- Manganese sulfate
Sold here with manganese: Manganese Sulfate by Zetryl Chem (31 percent manganese), Tierramino MN by Unilox Far East Resources (7 0 0 with 12 percent manganese), Multimate by Agway (4 0 0 with 4.5 percent sulfur, 2.8 percent zinc and 1.8 percent manganese) and Nutri Tabble Meta Foliar by NS Northern Organic Fertilizer (12 percent zinc, 9 percent sulfur, 2 percent magnesium and 1.2 percent manganese). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to foliar fertilizer, and the page on manganese deficiency in every crop.
To keep it away, do not lime beyond pH 6.5. Test the soil every two or three years.
A soil test is the surest check for any string bean nutrient deficiency. Before you buy, ask your Municipal Agriculture Office where to send a soil sample. The DA regional soil laboratories test soil, and the result says how much of each fertilizer your sitaw needs. That saves money, because extra fertilizer is money lost.
Open the Nutrient Deficiency Finder, pick sitaw, say where the leaves changed first and what you see, and get the fertilizers sold here that fix it.
- Anee, the smart farm technician, reads a photo of the leaf
- The cropping calendar dates every fertilizer application of your season
String bean nutrient deficiency questions
Why are my sitaw leaves turning yellow?
What fertilizer fixes nitrogen deficiency in string bean?
What fertilizer fixes phosphorus deficiency in string bean?
What fertilizer fixes potassium deficiency in string bean?
How do I know which nutrient my sitaw lacks?
Find the missing nutrient and fix it
With Libre + Anee, read the whole guide: how to tell the deficiency from look alikes, how to be sure, what to apply, and the fertilizers sold here that supply it.
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