If you spot the signs of such disease, then mixing a household item in water for a spray can help stop it from spreading. What household item can help struggling plants in autumn? Bicarbonate of soda can be a useful tool in the fight against fungal infection in plants, when diluted with water and sprayed onto a plant. Richard Barker, horticultural expert and commercial director of LBS Horticulture, urges gardeners to be careful if using the bicarbonate of soda spray. "Avoid using baking soda on the soil of plants, as it can raise the alkalinity of the soil too high for the majority of plants.