The Blueberry News – July 2019

FloridaBlueberryGrowers.org The Blueberry News | 35

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SELECTIVE POSTEMERGENCE HERBICIDES

Carfentrazone (Aim) controls broadleaf weeds and may cause a little

browning around the edges of grass weeds, but will not control grass

weeds. Carfentrazone is included in many products that are registered

for homeowners lawn herbicides.

Halosulfuron (Sandea) is one of the best options for postemergence

control of nutsedge, broadleaf, and grass weeds. Broadleaf weeds that are

controlled are ragweed parthenium, pigweed species, and wild radish.

Halsoulfuron also provide preemergence weed control. Discussions

with growers conclude that ‘Prima Donna’, ‘Scintilla’, ‘Springhigh’ are

more susceptible to crop injury than other cultivars, ‘Emerald’ and

‘Jewel’. Use halosulfuron on a small area if a cultivar is not listed here.

Clethodim (Poast), fluazifop (Fusilade), and sethoxydim (Select

Max) are herbicides that control grass weeds only. During the summer,

all of these herbicides can be used, but when berries are present in the

spring selection should be based on the preharvest interval of each

formulation. The preharvest interval can vary by 1 to 21 days for each

formulation. The Fusilade label has been changed to include bearing

plants so now all these can be used on bearing and nonbearing bushes.

NONSELECTIVE POSTEMERGENCE HERBICIDES

Glyphosate (Roundup) translocates through the plants, which can

be problematic because it can be absorbed by the blueberry bush

and translocated to the growing tips and cause injury. However,

translocation is important for the control of perennial weeds such as

dogfennel and nutsedge.

Paraquat (Gramoxone Inteon) provides control of broadleaf and

grass weeds. New regulations for paraquat are covered in another

article. Possible alternatives with similar weed control and use patterns

are diquat (Reglone Desiccant), glufosinate (Rely), pelargonic acid

(Scythe). These herbicides do not translocate so injury to blueberry

bushes is limited to the lower leaves that are sprayed with the

herbicide. Perennial weeds will have the tops removed, but the below-

ground structures will survive and regrowth will occur.

ORGANIC HERBICIDES

All organic herbicides registered in blueberries are nonselective

and only control the portion of the plant that is sprayed by the

herbicide. Many of the herbicides remove the outer layer of the leaf

cuticle layer resulting in water loss and death or remove the cell

membrane. During the summer, the weeds will have a thicker cuticle

so multiple applications may be needed. Organic herbicides include

ammonium nonanoate (Axxe), caprylic acid + capric acid (Suppress),

citric acid, and eugenol (Weed Slayer)

IMPROVING CONTROL

Factors that can improve the efficacy of postemergence include:

proper identification of the weed, inclusion of a surfactant (nonionic,

crop oil, fertilizer) according to the label, application when weeds

are small and succulent to improve uptake, complete coverage of the

weed, and observing the restriction before the next rain or irrigation

event.

NONCHEMICAL

Mowing weeds can be effective, however, if the plants are

developing seeds then use a bag or blow the seeds away from the crop

row. Weeds can be hand remove or hoed, but for perennial weeds dig

the underground structures to prevent regrowth.

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CREDIT

by PETER DITMAR, Associate Professor,

UF Horticultural Sciences Department