Growing strawberries in the tropics is not the easiest thing to do as we’ve previously addressed in several articles. But with patience and some perseverance, it can be done successfully, and you will be well rewarded with fruit that has a nice aroma, bright red colour, juicy texture, sweetness, and health benefits.
If you don’t take proper care of your strawberries and provide then with the optimum growing environment, the plant will get stressed and show different kinds of symptoms. Among the different symptoms, the browning leaf of the strawberry leaves indicates the most serious problems.
Strawberry leaves start turning brown for a number of different reasons. There are four most common reasons, and they are improper watering, nutrient deficiency, fungal and bacterial diseases, and attacks by nematodes. It’s important to identify the right cause of the browning of the leaves otherwise the wrong treatment may do further harm to your plant.
In this article, I will try to help you to identify the reason and provide the most actionable solution that can revive your strawberry plants. But let me first address a question that is often asked, and this is “Should I cut off the leaves that turn brown?”
The answer to that question is a definite yes. You should cut off any leaves that have turned brown and destroy them carefully. That means burning them or placing them in a plastic bag and disposing in in a trash can.
Never put the brown leaves in a compost heap or let them come into contact with healthy plants, because if the leaves have been affected by a fungus, it will spread to healthy plants. And remember to disinfect your secateurs after cutting off the leaves.
So let’s now discuss the four most common reasons in more detail:
1. Improper Watering
This is the most common case of leaves turning brown and is fortunately the easiest to rectify. Both over and underwatering can cause the browning leaves of the strawberry plant. Strawberries have a shallow root system, so the roots dry out easily during hot weather. As a result, wilting takes place and plant’s leaves become droopy and start yellowing.
In contrast, overwatering suffocates the plant roots and that causes root rot. And the damaged root can’t provide the required nutrients and water to the plant. Finally, the leaves turn brown.
It’s important to know the proper watering schedule to revive over or underwatered strawberry plants. The basic rule of watering is to provide water in such a way that the soil doesn’t dry out completely or become soggy.
How much water a strawberry plant needs depends entirely on local conditions, temperature, humidity, wind (windy days dry out the plants more quickly), soil type, whether it has rained recently and whether it is well mulched.
So it’s not possible to give an hard and fast rules about water quantity. Just ensure the soil never dries out or becomes too wet.
Here’s a short checklist that may help you to avoid improper watering issues:
- Check the soil before watering. Use a moisture meter or poke the finger deep into the soil to feel the moisture.
- Only apply water overhead for new plants that aren’t yet fruiting. Don’t water overhead once fruit forms as it may rot the fruits.
- Preferably use drip irrigation or a soaker-hoses for watering established strawberry plants.
- Apply organic mulch around the plant.
- Apply water as early as possible in the day. Don’t water in the evening.
- Plant heat and drought tolerant varieties such as Camarosa, Sweet Charlie Chandler, Sequoia, Loran, Camino Real, and Seascape.
2. Nutrient Deficiency
Nitrogen is one of the major components of chlorophyll and you may know, chlorophyll is the green pigment that absorbs light and makes food for plants. So, if your strawberry plants don’t get the required amount of nitrogen, the leaves can turn yellow to brown. But don’t overdo the nitrogen because your plants still need phosphorus and potassium to fruit properly.
A complete NPK fertilizer with a reasonably high nitrogen level needs to be used. If you can find one with trace elements as well, that will be beneficial for the overall plant health. You can use organic fertilizers as well, but you will need a larger quantity of organic fertilizer compared to inorganic fertilizers.
To ensure that the nutrients in the fertilizer can be taken up by the plant, it’s important ti check the soil pH with a soil pH meter. If the soil pH is lower than 4, you should apply some garden lime to increase the soil pH because acidic soil prevents the uptake of nitrogen.
5.8 to 6.2 is the optimum pH for growing strawberries. If the soil pH remains in the optimum range, then you shouldn’t have any problems producing fruit with a good NPK fertilizer or well-balanced organic fertilizer.
3. Fungal & Bacterial Diseases
Verticillium wilt, leaf spot, leaf scorch, and leaf blight are the most common fungal and bacterial diseases that will cause the leaves of strawberries to go brown.
Verticillium wilt is a root and crown disease that is caused by a soil-borne pathogen called Verticillium albo-atrum. It affects the plant when the temperature and the day length increase. The leaves of the strawberry plants become browning along the edges and between the veins.
The best way to prevent this is to use sterilized fungus-free soil or treat your existing soil by applying fungicide before planting and never let the soil dry out completely. Also, you can spray a preventive fungicide to prevent the verticillium wilt if you discover that this is prevalent in your locality.
Leaf spot is another fungal disease, this one caused by Mycosphaerella fragariae. It can be diagnosed fairly easily because the strawberry leaves show purple spots with white or brown centers. It attacks the new leaves of strawberry plants and occurs in cooler tropical localities that still experience humid weather.
For those living in localities where leaf spot is a problem, it’s best to cultivate resistant varieties such as Crimson King, Glooscap, Earliglow, Ogallala, and Ozark Beauty, and apply preventive fungicide to protect the plant from this fungus.
Diplocarpon earlianum is the culprit behind leaf scorch. Dark purple spots without a white or brown center appear on the upper leaves of the strawberry. In severe conditions, the spots turn the leaves brown and kill the leaves completely.
If leaf scorch becomes a problem, you’ll have to apply fungicide to control and cut off all affected leaves with clean tools.
Leaf blight is another leaf disease that is caused by a fungus called Phomopsis obscurans. The Circular light brown spots with reddish-purple borders appear on the leaves of the strawberry and gradually take over the whole leaf.
As with leaf scorch, you’ll need to prune the plant and apply fungicide to control the disease. Reducing the number of leaves to help improve air circulation can also help.
Types of Fungicides
First, prune the affected leaves and increase the air circulation. Must destroy the affected leaves safely. Don’t mist or spray water on the plant in the evening. Because wet conditions at night can accelerate the growth of fungus. Apply Copper, Sulfur, Myclobutanil, or Neem Oil containing fungicide.
There are a wide range of copper and sulfur fungicides available as well as steroid demethylation inhibitors like Myclobutanil. For those looking for a non-toxic solution, you can make a homemade fungicide by mixing four tablespoons of baking soda or potassium bicarbonate into a gallon of water and spray on both the upper and lower sides of the leaves.
The homemade solution may not be as effective as the chemical options, but many growers have reported satisfactory results if used frequently. Spray in the morning, not at night.
Strawberry foliar nematode or strawberry crimp nematode disease is caused by a plant pathogenic nematode called Aphelenchoides fragariae. V-shaped, water-soaked lesions and necrotic blotches appear on the leaves.
The only way to control nematodes is to heat the soil at 45°C for 20-30 minutes before planting. If this is not done, or is not possible to do, then treatment with a broad spectrum nematicide like ZeroTol, Vapam or Larvicide is the only option.