Predicting weed emergence dynamics can help farmers to plan more effective
weed control. The hydrothermal time concept has been used to model emergence
as a function of temperature and water potential. Application of this
concept is possible if the specific biological thresholds are known. This
article provides a data set of base temperature and water potential of eight
maize weeds (velvetleaf, redroot pigweed, common lambsquarters, large
crabgrass, barnyardgrass, yellow foxtail, green foxtail, and johnsongrass).
For five of these species, two ecotypes from two extreme regions of the
predominant maize-growing area in Italy (Veneto and Tuscany), were collected
and compared to check possible differences that may arise from using the
same thresholds for different populations. Seedling emergence of velvetleaf
and johnsongrass were modeled using three different approaches: (1) thermal
time calculated assuming 5 C as base temperature for both species; (2)
thermal time using the specific estimated base temperatures; and (3)
hydrothermal time using the specific, estimated base temperatures and water
potentials. All the species had base temperatures greater than 10 C, with
the exception of velvetleaf (3.9 to 4.4 C) and common lambsquarters (2.0 to
2.6 C). All species showed a calculated base-water potential equal or up to
−1.00 MPa. The thresholds of the two ecotypes were similar for all the
studied species, with the exception of redroot pigweed, for which the Veneto
ecotype showed a water potential lower than −0.41 MPa, whereas it was −0.62
MPa for the Tuscany ecotype. Similar thresholds have been found to be useful
in hydrothermal time models covering two climatic regions where maize is
grown in Italy. Furthermore, a comparison between the use of specific,
estimated, and common thresholds for modeling weed emergence showed that,
for a better determination of weed control timing, it is often necessary to
estimate the specific thresholds.