Roundup Application Time of Day

Farmers and applicators claimed reduced weed control with early morning or late evening applications of Roundup.Does light or dew effect Roundup performance?

Roundup Application Time of DayMaterial and Methods

Roundup rate: 1 pt/A

Application Stages: P: 4-8 inch velvetleaf and Palmer amaranthLP: 6-12 inch velvetleaf and Palmer amaranth

Application time of day:6 am, 10 am, 1:30 pm, 5 pm, 9 pm

Time of Day: 6AM 10 AM 1:30 PM 5 PM 9 PM

Date -------------------August 19-----------------Temperature 57 F 73 F 79 F 83 F 68 F Humidity 70% 55% 45% 42% 80% Dew Yes No No No No Palmer amaranth ----------------1 to 8 inches-----------------Velvetleaf ----------------1 to 4 inches-----------------Sunrise/Sunset 6:42 am-----------------------------8:20 pm

Early Postemergence Application Information

Time of Day: 6AM 10 AM 1:30 PM 5 PM 9 PM

Date -------------------August 23-----------------Temperature 64 F 78 F 86 F 89 F 64 F Humidity 96% 67% 59% 33% 81% Dew Yes No No No No Palmer amaranth ----------------4 to 12 inches---------------Velvetleaf -----------------2 to 8 inches----------------Sunrise/Sunset 6:45 am-----------------------------8:18 pm

Late Postemergence Application Information

The influence of application time of day on Roundup performance, Manhattan, KS, 1999.

Application Palmer amaranth VelvetleafTime of Day Post LP Post LP

--------------(% control)-------------

6:00 am 96 85 96 47 10:00 am 99 100 99 99 1:30 pm 100 100 99 99 5:00 pm 100 99 97 97 9:00 pm 99 88 95 47

LSD 3 9

Postemergence – 6am

Postemergence - 10 am

Postemergence - 1:30 pm

Postemergence - 5 pm

Postemergence - 9 pm

Late Postemergence - 6 am

Late Postemergence - 10 am

Late Postermegence - 1:30 pm

Late Postemergence - 5 pm

Late Postemergence - 9 pm

Application Time of Day

Weed control with Roundup was less when applied pre-dawn or post sundown than during the middle of the day.Possible reasons:

presence of dewlight influence on physiological interactionsplant leaf orientation

Day:

Night:

Velvetleaf Palmer amaranth

Leaf Orientation During the Day and at Night