Herbicide Application During Rainy Weather

By Ramdas Kanissery

Finding the right time to apply post-emergent herbicides for controlling weeds in citrus groves is challenging in the summer months due to frequent rain. Rainy conditions delay grove maintenance, including herbicide spraying, while also impacting the effectiveness of the herbicides. Monitoring weather forecasts and identifying optimal conditions for herbicide applications can help achieve the best results. Below are some tips for timing herbicide applications in citrus groves during rainy seasons.

HERBICIDE APPLICATION BEFORE RAIN

To apply herbicides before it rains, ensure there is enough time for the herbicide to dry and be absorbed by the plants. This necessary interval between application and subsequent rainfall, known as the rainfast period, is crucial for effective post-emergent herbicide performance. Rainfall shortly after spraying can reduce herbicide absorption, translocation and weed control. If rain occurs before the herbicide becomes rainfast, its performance will be compromised. Check the product label for specific rainfast requirements of each herbicide.

Table 1 lists the rainfast periods for various post-emergent herbicides used in citrus groves based on label recommendations.

Table 1: Rainfast periods for post-emergent herbicides used in citrus

Herbicide Product(s)	Active Ingredient	Rainfast Period* (Hours)
Aim	Carfentrazone	1
Gramoxone SL	Paraquat	0.5
Roundup PowerMAX	Glyphosate	0.5
Roundup WeatherMAX	Glyphosate	0.5
Scout Rely 280	Glyphosate	4
Embed Extra	2,4-D	6+
Poast	Sethoxydim	1
Fusilade DX	Fluazifop-butyl	1
Treevix	Saflufenacil	1

HERBICIDE APPLICATION AFTER RAIN

Avoid spraying immediately after rain. Wait until the leaves are dry before applying herbicides. Spraying on wet leaves can wash away the herbicide, dilute it and reduce its effectiveness. Make sure no additional rain is expected soon after application, as quick sprays between showers are not effective. Herbicides work best when applied to dry leaves, allowing proper absorption.

CONSIDER WIND

During rainy seasons, check wind conditions before applying herbicides. Spraying in windy conditions can cause herbicide drift, potentially damaging citrus trees. Avoid spraying if the wind has picked up ahead of the rain.

By keeping these strategies in mind, growers can improve the effectiveness of herbicide applications in citrus groves despite rainy weather.

Ramdas Kanissery is an assistant professor at the University of Florida Institute of Food and Agricultural Sciences Southwest Florida Research and Education Center in Immokalee.

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