Vines on Coffee
Figure 29. Vines like morning glory are the most serious weed problem in
dry areas.
Volunteer coffee seedlings are a particular problem in mechanically
harvested orchards.
Volunteer Coffee
Figure 30. Volunteer coffee seedlings can be a weed problem particularly
in mechanically harvested coffee. Easily controlled at this stage by
mechanical weeding or herbicides such as RoundUp or Gramoxone during the
spring weed control. Don't them grow through till harvest as they may be
too big.
Weed control costs are estimated to range from 3 to 10 percent of annual
growing costs, assuming that weeds are managed well and extensive hand
weeding does not become necessary (Fleming et al. 1998).
In the past, farmers have used mulch to protect the area under the tree from weed growth. Mulch materials used include coffee parchment skin, flat stones, macadamia nut husks, and dried grass. Mulches of organic materials are still used by organic farmers and others. Mulch should be kept at least 2 inches away from the trunk to avoid having any area on the trunk in continuous contact with moist material.
Most often today, artificial mulches are used as barriers to weed growth. Two common types are black plastic film (as used in pineapple fields) and black woven cloth ("weed cloth") that is permeable to water. Normally, weed cloth is laid before transplanting to keep weeds away from the area where the feeding roots are most numerous. During the dry season, mulch helps maintain soil moisture, particularly important at lower elevations. Hoeing or hand weeding is expensive, and mulches are a good way to minimize the expense of weed control during the first year. Although hoeing was the most common weeding practice in the past, chemical weed control is almost universally practiced in coffee orchards in Hawaii, except in organic orchards, where string trimmers, hoeing, and even geese are used.
The advantages of chemical weed control (herbicides) over hoeing are that it is faster, it is less expensive because less labor is needed, it minimizes soil erosion on sloping land, and it has greater efficiency during rainy weather because the soil is not disturbed to bring buried weed seeds to the surface.
Mowing is feasible in coffee orchards provided the orchard floor is properly prepared by removing rocks and uneven sections. Planting a cover crop will produce a uniform groundcover that will be more efficient to mow than a mixed, volunteer groundcover. Allowing volunteer groundcovers and keeping them mowed is a common practice that works well provided there are no vines to tangle in the mower or climb the coffee trees. Undesirable weed species that occur in the volunteer groundcover should be mown or otherwise controlled before they produce seeds.
Some herbicides registered for use in coffee crops are described below,
but the person applying the pesticide must read the pesticide's label to
learn about application rates, limitations, and use precautions. The
label also specifies the weeds that the herbicide is effective against.
One way to find out which pesticides (herbicides, insecticides, and
fungicides) are registered for coffee is to check CTAHR's Hawaii Pesticide
Information Retrieval System (HPIRS) at our Web site,
Postemergence herbicides are applied to weeds after they have germinated.
GramoxoneR (paraquat) is a contact herbicide effective against many annual
weeds; it will damage coffee leaves and green stems. You must be a
certified applicator to purchase this product. RoundupR (glyphosate) is a
systemic herbicide effective against most annual and perennial weeds; it
may kill the coffee plant if allowed to contact coffee leaves or green
stems. Fusilade 2000R (fluazifop-butyl) is a systemic herbicide effective
against certain annual and perennial grasses.
Orchards in dry areas rely heavily on two broad-spectrum, postemergence
herbicides, paraquat and glyphosate. Their efficacy against a wide range
of weed species and growth stages allows flexibility regarding the timing
of application; this is especially important to growers who cannot keep
ahead of weeds. The effect of Roundup can be enhanced by mixing it,
according to label directions, with ammonium sulfate or a postemergence
herbicide called ScytheR, which has the active ingredient pelargonic
acid.
Pre-emergence herbicides are applied before weeds germinate, usually to
bare soil. Goal 1.6ER (oxyfluorfen) controls certain annual broadleaf
weeds, but its continual use encourages perennial broadleaf weeds.
SurflanR (oryzalin) controls certain annual grasses and broadleaf
weeds.
Preemergence herbicides prevent weed seeds from sprouting. In newly
established coffee orchards, they are sprayed beneath trees in rows
between mown ground-cover alleys to minimize maintenance costs. Mowing and
use of selective herbicides are both usually needed to maintain
groundcovers.
A number of groundcover species can be used in coffee. In Kona, a dwarf
"wandering Jew" (Tradescantia boli-vaensis) is seen.
Wandering Jew
Several species have been evaluated by CTAHR for dry areas, although none
are in wide use yet. A demonstration planting (Evensen, 1997) identified
species of perennial and annual cover crops that establish effective soil
cover, minimize soil surface exposure, and thus provide protection against
soil loss on highly erodible lands. The planting indicated that the
drought-tolerant perennial cover crops 'Tropic Lalo' (Paspalum
hieronymii), Rhodes grass (Chloris gayana), Kline grass
(Panicum coloratum), buffelgrass (Cenchrus ciliaris), and
possibly bermudagrass (Cynodon dactylon) are well adapted to
low-rainfall areas. The planting suggested that narrowleaf carpetgrass
(Axonopus affinis) and perennial peanut (Arachis pintoi) are
not good for dry conditions because they grow slowly and do not rapidly
protect the soil or suppress weeds in their early growth stages. Perennial
peanut should do well if planted at the beginning of the rainy season or
irrigated during establishment.
Peanut
Buffelgrass
Small grains, such as ryegrass (Lolium multiflorum), oat (Avena
sativa), and rye grain (Secale cereale), were also evaluated as
temporary cover crops for protecting the soil during the rainy season from
November to April (in areas other than Kona), which is generally the most
erosive and weedy period of the year, and then dying out during the summer
months. This may be an attractive option for plantations that face summer
water shortages and have concerns about competition for water between the
coffee and the cover crop.
Ryegrass
Caution is advised in selecting a groundcover for coffee orchards, because
research has yet to determine if any of the cover crops mentioned above
hosts the Kona coffee root-knot nematode. Rhodes grass and buffelgrass are
generally not hosts of other root-knot nematode species, while 'Tropic
Lalo' is suspect because it is related to hilograss, a known host of the
Kona coffee root-knot nematode.
Postemergence herbicides
Pre-emergence herbicides
Groundcovers and cover crops
Figure 31. View of 'dwarf wandering Jew' in a coffee orchard in
Kona.
Wandering Jew Close up
Figure 32. Close up of this 'dwarf wandering Jew'.
It is a relative of honohono (Commelina diffusa). Orchard grass
(Dactylis species) is also common in Kona orchards.
Figure 33. Good stand of perennial peanut. Drought tolerant once
established though weed suppression is not a good as best grass.
Peanut Close Up
Figure 34. Close up of perennial peanut, reseeds itself, but needs
inoculation for best growth, sensitive to soil pH over 7 and high soil
phosphorus. Either can cause poor growth from induced Fe deficiency (young
leaves are white).
An important benefit of cover crops is the elimination or reduction of
weed control measures, including herbicide applications. While several of
the cover crops studied in the CTAHR dry-site demonstrations provided
adequate soil erosion control, they were not all effective in controlling
weed infestation. Vigorous, thick grasses with a low-lying canopy, such as
Rhodes grass and Kline grass, were most effective in suppressing the
proliferation of invading weeds. However, these tall grasses required
frequent mowing (every 2-3 months) to control their height to the extent
desired by the plantation (i.e., less than about 1 ft high). The somewhat
less vigorous buffelgrass provided a good compromise, being lower growing
and requiring little or no mowing. In addition, buffelgrass was the most
drought tolerant of the cover crop species in the demonstration.
Figure 35. A very drought tolerant, clump grass.
'Tropic Lalo' paspalum is lower growing and may not require mowing to
remain at the desired height under dry conditions. But it must be
propagated with sprigs and thus may be more expensive to plant than the
other species, which can be established from seed.
Figure 36. Winter 'Alamo' ryegrass, is one of several annual small grains
that can be planted at the beginning of the rainy season to prevent
erosion and weeds but dies in dry season. Must be planted each
year.
The Natural Resources Conservation Service is a source of information on
cover crops suited to various areas.
