Vol. 54—2000 - NorthEastern Weed Science Society

Crop leaf and weed leaf size were estimated on a scale of 1-10 were 1 was very fine grass like
foliage and 10 was very large tropical like foliage. The success or failure of hand wee ding as a
function of crop to weed leaf size ratios was evaluated by estimating weed numbers, crop size and
crop loss.
Herbicides were applied to pots on the day of transplanting as directed sprays to the
surrounding soil with minimal crop interception. Three herbicides were evaluated for efficacy 4, 8 and
16 weeks after treatment (wat) Gallery (isoxaben [N-[3-(I-ethyl-I-methylpropyl)- 5-isoxazolyl] -2,6­
dimeth-oxybenzamide D,Dacthal (DCP AIdimethyl 2,3,5,6-tetrachloro-I,4- benzenedicarboxylate D
and Roundup (glyphosate [N-(phosphonomethyl)g1ycine] were applied at label rates with a four
gallon Solo backpack pump sprayer delivering I.5 gaVIOOOIt' at 30psi.
RESULTS AND DISCUSSION
The introductory survey revealed that nearly all receipted plugs harbored various weeds; both
small and large in stature (Table 1). The principal weeds removed at transplanting were bittercress,
oxalis, clover, chickweed. mouse-ear chickweed and dandelion. Plantain, annual and Kentucky
bluegrass and crabgrass appeared far less frequently in the plugs but were dispersed from other
sources during the course of the season. Handweeding at the time of transplant effectively removed
most but not all of these weeds. Considerable crop damage and crop loss accompanied weed removal
at transplant; employees reported that they could not distinguish weed from crop or were unable to
remove one from the other without tearing. Crops were given a strength estimation basedon their
rate of growth from the plug. Crop regrowth strength did not appearto influence crop loss due to
handweeding; rapidly growing 'strong' crops such as Achillea and Veronica suffered losses of 25 and
75%. respectively; while slower growing crops such as Lavendula or Nepeta were identically
damaged. Nearly all the weeds encountered here were able to resume growth before the crop; many
of them were able to continue growth after crop growth slowed or reverted to flowering. However
the rapidity of crop growth during the first two to four weeks after transplant effectively limited
growth of many of these weeds. Only a few weeds exhibited growth concomitantly with the crop.
Crop size was markedly suppressed by handweeding damage and/or weed growth; 2.5 inch plugs
were often reduced to less than 1 inch; 1 inch circular plugs were often less than 1/2 inch diameter.
Crop loss ranged from none in very aggressive crops (or crops that had broken dormancy prior to
receipt i.e. Baptisia, Geranium, Hemerocallis, Hosta) to 75% in slower growing or small stature crops
i.e. Nepeta, Thymus, Veronica.
In an attempt to explain why handweeding proved both difficult and damaging; crop and weed
plants were given an estimation of leaf sizefor those leaves evident at or within 2 weeks of
transplanting., Table 2. Tiny leaved crops such as Tunica or Thymus were often indistinguishable
from tiny leaved weeds such as carpetweed or starwort and share the same leaf size estimate. A
similar pattern held true from small leaved plants such as Veronica and mouse-ear chickweed,;
moderate sized plants such as Oenothera and dandelion and large leaved plants such as Hosta and
plantain. Developing a ratio of crop leaf size to weed leaf size (c/w) demonstrated the similarities
between crop and weed and assisted growers in training empJoyees in handweeding, Table 3. The
crop size at maturity reflected the ability of the crop to outgrowth both handweeding damage and
weeds and had little bearing on the c1w ratio. Crop losses were greatest where the C/Wratio was
small; crops with the same leaf size were routinely misidentified whether large or small.For example
removing bittercress from Erodium or chickweed from Veronica resulted in 80% or greater crop loss;
identical damage occurred removing plantain from Rudebeckia or Hosta Successful handweeding
with minimal damage occurred only when c1w was great and the difference between leaf sizes
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